diff --git a/crates/engine/src/commands.rs b/crates/engine/src/commands.rs
index 9000b71b0e..1996bcd793 100644
--- a/crates/engine/src/commands.rs
+++ b/crates/engine/src/commands.rs
@@ -231,6 +231,16 @@ pub const COMMANDS: &[CommandSpec] = &[
     // Split view (Acrobat's Window ▸ Split): the current document in two panes, or back to one;
     // a tab's right-click menu also splits right or down with any tab.
     c("view.split", "Split", VIEW, Some(Shortcut::cmd("\\")), Document, "columns-2"),
+    // A document can hide the toolbars, menu and panels (ISO 32000-2 Table 147); this brings them
+    // back for its tab, and with nothing hidden hides them.
+    c(
+        "view.toggle_interface",
+        "Show or hide toolbars and panels",
+        VIEW,
+        Some(Shortcut { command: false, shift: false, mac_ctrl: false, key: "F8" }),
+        Document,
+        "panel-left",
+    ),
     // Browsers' tab keys (#1542): Ctrl+Tab on every platform, ⌃Tab rather than ⌘Tab on macOS,
     // where the system takes ⌘Tab. They follow the tabs' order on screen and wrap around, and
     // also run from Combine files, which has no document open.
diff --git a/crates/ui-egui/src/app.rs b/crates/ui-egui/src/app.rs
index 0c72f09e4b..956a6238bf 100644
--- a/crates/ui-egui/src/app.rs
+++ b/crates/ui-egui/src/app.rs
@@ -305,6 +305,7 @@ impl PdfCraftApp {
             community_card_closed: false,
             pending_link: None,
             pending_full_screen: None,
+            pending_window: None,
             pending_remote_link: None,
             protect_draft: Default::default(),
             text_style_draft: Default::default(),
@@ -779,7 +780,12 @@ impl PdfCraftApp {
             window_controls::resize_edges(&ctx);
         }
         chrome::tab_strip(self, ui);
-        chrome::mode_bar(self, ui);
+        // A document can hide the toolbars, the menu and the panels around it in its tab (ISO
+        // 32000-2 Table 147); the tab strip stays, and F8 brings the rest back (`viewer_prefs`).
+        let hidden = self.hidden_interface();
+        if !hidden.mode_bar(self.native_menu.is_some()) {
+            chrome::mode_bar(self, ui);
+        }
         // Another mode or the Home tab puts the OCR Verify screen away, as Exit does; Correct
         // recognized text brings it back with its review as it was.
         if self.ocr_verify.open && (self.active.is_none() || self.ocr_verify.shown_in.is_some_and(|m| m != self.mode)) {
@@ -806,15 +812,19 @@ impl PdfCraftApp {
         if self.all_tools_full && self.all_tools_tab != self.shown_tab() {
             self.all_tools_full = false;
         }
-        side_panels::show(self, ui);
+        if !hidden.window_ui {
+            side_panels::show(self, ui);
+        }
         let t = theme::Tokens::get(&ctx);
         egui::CentralPanel::default().frame(egui::Frame::NONE.fill(t.pasteboard)).show(ui, |ui| {
-            if self.mode == Mode::AllTools && self.all_tools_full {
+            if self.mode == Mode::AllTools && self.all_tools_full && !hidden.window_ui {
                 all_tools_ui::show(self, ui);
             } else {
                 panes::page_area(self, ui);
             }
         });
+        // FitWindow and CenterWindow, once the document just opened is laid out.
+        self.window_preferences_frame(&ctx);
         self.process_pending_edits();
         palette::show(self, &ctx);
         dialogs::show(self, &ctx);
diff --git a/crates/ui-egui/src/app/files.rs b/crates/ui-egui/src/app/files.rs
index ef3d31a256..a59f5b19c0 100644
--- a/crates/ui-egui/src/app/files.rs
+++ b/crates/ui-egui/src/app/files.rs
@@ -351,9 +351,11 @@ impl PdfCraftApp {
             self.active = Some(self.views.len() - 1);
         }
         self.apply_initial_view(self.views.len() - 1, &initial);
-        // Where the reader left off wins over the file's own initial view (#1767).
+        self.apply_viewer_preferences(self.views.len() - 1, &initial, activate);
+        // Where the reader left off wins over the file's own initial view and the zoom its
+        // viewer preferences open at (#1767).
         self.apply_last_view(self.views.len() - 1);
-        // After both, so full screen shows one fitted page and leaving it comes back to them.
+        // After all of them, so full screen shows one fitted page and leaving it comes back to them.
         if self.full_screen
             && let Some(view) = self.views.last_mut()
         {
diff --git a/crates/ui-egui/src/canvas.rs b/crates/ui-egui/src/canvas.rs
index 983af1d993..171460fcc1 100644
--- a/crates/ui-egui/src/canvas.rs
+++ b/crates/ui-egui/src/canvas.rs
@@ -561,6 +561,9 @@ pub struct DocView {
     pub flash: Option<(usize, [f32; 4], f64)>,
     /// Compare files: differences shaded on this document's pages (page, user-space box, colour).
     pub compare_marks: Vec<(usize, [f32; 4], Color32)>,
+    /// The interface the document hid in this tab, and what is hidden now (ISO 32000-2 Table 147
+    /// `HideToolbar`, `HideMenubar`, `HideWindowUI`). Never saved.
+    pub interface: crate::viewer_prefs::TabInterface,
     /// Full screen (Acrobat's Full Screen Mode): the display saved on entering it, while the view
     /// shows one page or spread at a time, fitted to the screen. `None` outside full screen.
     presentation: Option<SavedDisplay>,
@@ -1039,6 +1042,7 @@ impl DocView {
             single_edges: None,
             flash: None,
             compare_marks: Vec::new(),
+            interface: Default::default(),
             presentation: None,
             pages: HashMap::new(),
             errors: HashMap::new(),
@@ -1214,6 +1218,8 @@ impl DocView {
         fresh.snapshot = self.snapshot.clone();
         fresh.close_requested = self.close_requested;
         fresh.cover = self.cover;
+        // What the document asked to hide, and what is hidden now (F8), belong to the tab.
+        fresh.interface = self.interface;
         // Still presenting, with the display to go back to on leaving.
         fresh.presentation = self.presentation.take();
         fresh.back = std::mem::take(&mut self.back);
@@ -2609,6 +2615,11 @@ fn page_scroll_area(ui: &egui::Ui, view: &mut DocView, geometry: &ScrollGeometry
     // Every scroll here asks for no animation. An animated area would still queue a zero-length
     // offset target for the next frame, which overwrites the jump a page turn just set.
     scroll = scroll.animated(false);
+    // A document that hides the window's interface (`HideWindowUI`) hides the scroll bars too;
+    // the wheel, keys and Hand tool still scroll.
+    if view.interface.hidden.window_ui {
+        scroll = scroll.scroll_bar_visibility(egui::scroll_area::ScrollBarVisibility::AlwaysHidden);
+    }
     // A newly opened document starts at the top. eframe saves egui's memory with the settings
     // and document ids start again at 1 every launch, so the offset stored under this id can be
     // where an earlier session left another document.
@@ -3721,7 +3732,8 @@ fn apply_frame_requests(app: &mut PdfCraftApp, index: usize, ui: &mut egui::Ui,
     }
     // Read mode hides the tools (#2646), and full screen is the page and nothing else (#1459);
     // the quick tools come back with the window.
-    if app.mode != crate::Mode::Read && !app.full_screen {
+    // A document that hides the toolbars (`HideToolbar`) hides this one too.
+    if app.mode != crate::Mode::Read && !app.full_screen && !app.views.get(index).is_some_and(|v| v.interface.hidden.toolbar) {
         // The page nearest the left edge, whose margin the bar sits in.
         let page_left = app.views[index].screen_rects.iter().map(|(_, r)| r.left()).reduce(f32::min);
         quick_bar(app, avail, page_left, ui);
diff --git a/crates/ui-egui/src/canvas/tests.rs b/crates/ui-egui/src/canvas/tests.rs
index 1e8add9b2d..b710261ba8 100644
--- a/crates/ui-egui/src/canvas/tests.rs
+++ b/crates/ui-egui/src/canvas/tests.rs
@@ -2695,6 +2695,35 @@ fn a_moved_picture_is_drawn_from_the_fresh_raster_while_a_tile_is_still_stale()
     h.state_mut().views[0].tiles.clear();
 }
 
+/// Review on #4378: `FitWindow` measures the spread the view shows, its pages side by side
+/// and as tall as the taller one, with one page in a spread that has only one.
+#[test]
+fn first_page_now_measures_the_pages_in_the_spread() {
+    let page =
+        |width: f32, height: f32| pdfcraft_render::PageInfo { width, height, label: String::new(), crop: [0.0, 0.0, width, height], rotation: 0 };
+    let info = DocInfo { pages: vec![page(300.0, 400.0), page(600.0, 800.0), page(200.0, 500.0)], ..Default::default() };
+    let mut v = DocView::new(DocId(1), &info, ViewDefaults::default());
+    let one = v.first_page_now(&info).expect("a page");
+    assert_eq!((one.size, one.margins.x), (vec2(300.0 * PT, 400.0 * PT), 2.0 * SIDE));
+    v.set_display(PageLayout::TwoUp, false);
+    let gap = v.page_gap();
+    // [0, 1]: 300 + 600 wide, 800 high, one gap between them.
+    let spread = v.first_page_now(&info).expect("a spread");
+    assert_eq!((spread.size, spread.margins.x), (vec2(900.0 * PT, 800.0 * PT), 2.0 * SIDE + gap));
+    // [2] on its own at the end: one page, no gap.
+    v.current = 2;
+    let last = v.first_page_now(&info).expect("the last page");
+    assert_eq!((last.size, last.margins.x), (vec2(200.0 * PT, 500.0 * PT), 2.0 * SIDE));
+    // With a cover page: [0] alone, then [1, 2].
+    v.set_cover(true);
+    assert_eq!(v.first_page_now(&info).expect("a spread").size, vec2(800.0 * PT, 800.0 * PT));
+    v.current = 0;
+    let cover = v.first_page_now(&info).expect("the cover");
+    assert_eq!((cover.size, cover.margins.x), (vec2(300.0 * PT, 400.0 * PT), 2.0 * SIDE));
+    v.current = 9;
+    assert!(v.first_page_now(&info).is_none());
+}
+
 #[test]
 fn image_handles_account_for_document_and_view_rotation() {
     for page_rotation in [0, 90, 180, 270] {
diff --git a/crates/ui-egui/src/canvas/zoom.rs b/crates/ui-egui/src/canvas/zoom.rs
index ef1239110a..6c10fc4feb 100644
--- a/crates/ui-egui/src/canvas/zoom.rs
+++ b/crates/ui-egui/src/canvas/zoom.rs
@@ -140,6 +140,31 @@ impl DocView {
         self.layout == PageLayout::TwoUp
     }
 
+    /// The page (or spread) the view shows first, as `FitWindow` sizes the window to it
+    /// ([`crate::viewer_prefs::window_commands`]). `None` when there is no such page.
+    pub(crate) fn first_page_now(&self, info: &DocInfo) -> Option<crate::viewer_prefs::PageNow> {
+        info.pages.get(self.current)?;
+        // Two-page view shows the spread the page is in (a cover page on its own); the spread
+        // is as wide as its pages side by side and as tall as the taller one, as `layout`
+        // places it. The last spread of an odd page count has one page.
+        let (first, last) = if self.layout == PageLayout::TwoUp {
+            let first = self.spread_first(self.current);
+            (first, if self.cover && first == 0 { 0 } else { first.saturating_add(1) })
+        } else {
+            (self.current, self.current)
+        };
+        let sizes: Vec<(f32, f32)> =
+            info.pages.iter().skip(first).take(last.saturating_sub(first).saturating_add(1)).map(|p| self.display_size(p)).collect();
+        let w: f32 = sizes.iter().map(|s| s.0).sum();
+        let h = sizes.iter().map(|s| s.1).fold(0.0, f32::max);
+        let gap = self.page_gap() * sizes.len().saturating_sub(1) as f32;
+        Some(crate::viewer_prefs::PageNow {
+            size: vec2(w * PT, h * PT),
+            margins: vec2(2.0 * SIDE + gap, 2.0 * MARGIN),
+            zoom: (self.fit == Fit::None).then_some(self.zoom),
+        })
+    }
+
     /// Displayed page size in points for this view rotation.
     pub(super) fn display_size(&self, p: &pdfcraft_render::PageInfo) -> (f32, f32) {
         if self.rotation % 180 == 90 { (p.height, p.width) } else { (p.width, p.height) }
diff --git a/crates/ui-egui/src/chrome.rs b/crates/ui-egui/src/chrome.rs
index dba8419919..4cc264e7dc 100644
--- a/crates/ui-egui/src/chrome.rs
+++ b/crates/ui-egui/src/chrome.rs
@@ -588,19 +588,24 @@ const MODE_BAR_SEARCH_MIN: f32 = 140.0;
 
 pub fn mode_bar(app: &mut PdfCraftApp, ui: &mut egui::Ui) {
     let t = Tokens::get(ui.ctx());
+    // The document in the active tab may hide the menu or the tools (`crate::viewer_prefs`).
+    let hidden = app.hidden_interface();
     egui::Panel::top("mode_bar")
         .exact_size(48.0)
         .frame(egui::Frame::NONE.fill(t.chrome).inner_margin(egui::Margin::symmetric(10, 0)).stroke(Stroke::new(1.0, t.divider)))
         .show(ui, |ui| {
             ui.horizontal_centered(|ui| {
                 ui.spacing_mut().item_spacing.x = 2.0;
-                // The menus, unless the native macOS menu bar has them.
-                if app.native_menu.is_none() {
+                // The menus, unless the native macOS menu bar has them or the document hides them.
+                if app.native_menu.is_none() && !hidden.menubar {
                     app.menu_bar_ui(ui);
                     ui.add_space(6.0);
                     ui.painter().vline(ui.cursor().left(), ui.max_rect().y_range().shrink(12.0), Stroke::new(1.0, t.divider));
                     ui.add_space(10.0);
                 }
+                if hidden.toolbar {
+                    return;
+                }
                 // Acrobat's mode bar has no Read tab: reading is what the viewer does with no tool
                 // in use. Read mode (the panes hidden) stays a View command and a default workspace.
                 let modes = [(Mode::AllTools, "All tools"), (Mode::Edit, "Edit"), (Mode::Convert, "Convert"), (Mode::Sign, "E-Sign")];
diff --git a/crates/ui-egui/src/commands.rs b/crates/ui-egui/src/commands.rs
index 2d67ecd2b2..ac52586062 100644
--- a/crates/ui-egui/src/commands.rs
+++ b/crates/ui-egui/src/commands.rs
@@ -334,6 +334,7 @@ impl PdfCraftApp {
             }
             "view.read_mode" => self.switch_mode(if self.mode == Mode::Read { Mode::AllTools } else { Mode::Read }, false),
             "view.split" => self.toggle_split(),
+            crate::viewer_prefs::TOGGLE => self.toggle_interface(),
             "view.previous_view" | "view.next_view" => {
                 if let Some(v) = active.and_then(|i| self.views.get_mut(i)) {
                     return Some(v.view_history(id == "view.next_view"));
@@ -832,6 +833,11 @@ impl PdfCraftApp {
             if matches!(spec.id, "view.previous_view" | "view.next_view") && !self.command_enabled(spec) {
                 continue;
             }
+            // The OCR Verify screen keeps the window's toolbars and owns F8 and Shift+F8 (the next
+            // and previous word to review), so they don't show or hide the interface there.
+            if spec.id == crate::viewer_prefs::TOGGLE && self.ocr_verify.open {
+                continue;
+            }
             // A box typed into on the page (a paragraph being edited, added text) keeps Undo and
             // Redo only while it holds typing the page doesn't have, or Redo has typing to put
             // back; then they reach the document. ⌘⇧Z is also ⌘Z to the Undo shortcut, so a
diff --git a/crates/ui-egui/src/control/host.rs b/crates/ui-egui/src/control/host.rs
index cf8e5e7fcc..1373313a9c 100644
--- a/crates/ui-egui/src/control/host.rs
+++ b/crates/ui-egui/src/control/host.rs
@@ -152,6 +152,7 @@ impl Host for crate::PdfCraftApp {
             "tools_side": if self.side_panels.tools_on_right() { "right" } else { "left" },
             "rail_side": if self.side_panels.rail_on_right() { "right" } else { "left" },
             "right_panel": self.right.map(|r| format!("{r:?}")),
+            "hidden_interface": self.hidden_interface().to_json(),
             "dialog": self.dialog.map(|d| format!("{d:?}")),
             "palette_open": self.palette_open,
             "theme": format!("{:?}", self.theme),
diff --git a/crates/ui-egui/src/lib.rs b/crates/ui-egui/src/lib.rs
index c96765fda6..1da3a5fd18 100644
--- a/crates/ui-egui/src/lib.rs
+++ b/crates/ui-egui/src/lib.rs
@@ -63,6 +63,7 @@ pub use print_ui::{Handling as PrintHandling, OptionsSource, PrintDraft, Printer
 pub use redact_ui::{HiddenDraft, PagesDraft as RedactPagesDraft, RedactPrefs, SearchDraft as RedactSearchDraft, SearchMode as RedactSearchMode};
 pub mod i18n;
 pub mod theme;
+pub mod viewer_prefs;
 mod widgets;
 
 use pdfcraft_engine::{DocId, Session};
@@ -791,6 +792,9 @@ pub struct PdfCraftApp {
     /// A document just opened asks to be shown in Full Screen mode (`/PageMode /FullScreen`):
     /// the person is asked first, as in Acrobat, and this is the document waiting for the answer.
     pub pending_full_screen: Option<DocId>,
+    /// A document just opened asks for its window to fit its first page or to be centred
+    /// (`FitWindow`, `CenterWindow`): done once the page is laid out.
+    pub pending_window: Option<viewer_prefs::PendingWindow>,
     /// An absolute GoToR target waiting for approval, before any target-file I/O (#1364).
     pub pending_remote_link: Option<PendingRemoteLink>,
 }
diff --git a/crates/ui-egui/src/menus.rs b/crates/ui-egui/src/menus.rs
index 6987ba3b36..066a914e0d 100644
--- a/crates/ui-egui/src/menus.rs
+++ b/crates/ui-egui/src/menus.rs
@@ -173,7 +173,7 @@ const DISPLAY: &[&str] = &[
 const THEMES: &[&str] = &["view.theme.system", "view.theme.light", "view.theme.dark"];
 const PANES: &[&str] = &["view.side_panel", "view.tools_pane", "view.split"];
 const PANE_COMMANDS: &[&str] = &["comment.list", "form.fields", "ui.dock.reset"];
-const MODES: &[&str] = &["view.full_screen", "view.read_mode"];
+const MODES: &[&str] = &["view.full_screen", "view.read_mode", crate::viewer_prefs::TOGGLE];
 const PAGES: &[&str] = &[
     "page.organize",
     SEP,
diff --git a/crates/ui-egui/src/viewer_prefs.rs b/crates/ui-egui/src/viewer_prefs.rs
new file mode 100644
index 0000000000..8b6f023b6d
--- /dev/null
+++ b/crates/ui-egui/src/viewer_prefs.rs
@@ -0,0 +1,374 @@
+//! Viewer preferences that change the window and its interface when a document opens
+//! (ISO 32000-2 §12.2, Table 147): `HideToolbar`, `HideMenubar` and `HideWindowUI` hide parts of
+//! the interface for that document's tab, and `FitWindow` and `CenterWindow` size and place the
+//! window around its first page.
+//!
+//! The hidden interface is the tab's own and is never saved: another tab shows the usual
+//! interface, and the command [`TOGGLE`] (F8) brings it back, so a document can't leave the user
+//! without the toolbar, menu or panels.
+
+use egui::{Pos2, Rect, Vec2, ViewportCommand, vec2};
+
+/// The command that shows the interface a document hid, and hides it again.
+pub const TOGGLE: &str = "view.toggle_interface";
+
+/// Which parts of the interface are hidden in a document's tab.
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
+pub struct HiddenInterface {
+    /// The mode bar's tools: the mode tabs, Save, Print, Properties and the command search, and
+    /// the floating quick-action bar (`HideToolbar`).
+    pub toolbar: bool,
+    /// The menu bar (`HideMenubar`).
+    pub menubar: bool,
+    /// The right rail with its page navigation, the side panels and the document's scroll bars,
+    /// "leaving only the document's contents displayed" (`HideWindowUI`).
+    pub window_ui: bool,
+}
+
+impl HiddenInterface {
+    pub const NONE: Self = Self { toolbar: false, menubar: false, window_ui: false };
+    pub const ALL: Self = Self { toolbar: true, menubar: true, window_ui: true };
+
+    /// What a document's viewer preferences ask to hide.
+    pub fn asked_by(v: &pdfcraft_engine::InitialView) -> Self {
+        Self { toolbar: v.hide_toolbar, menubar: v.hide_menubar, window_ui: v.hide_window_ui }
+    }
+
+    pub fn any(self) -> bool {
+        self.toolbar || self.menubar || self.window_ui
+    }
+
+    /// The mode bar has nothing left to show: the tools are hidden, and so are the menus, by the
+    /// document or because the native macOS menu bar (`native_menu`) has them instead.
+    pub fn mode_bar(self, native_menu: bool) -> bool {
+        self.toolbar && (self.menubar || native_menu)
+    }
+
+    /// For the control channel's `ui.state`.
+    pub fn to_json(self) -> serde_json::Value {
+        serde_json::json!({ "toolbar": self.toolbar, "menubar": self.menubar, "window_ui": self.window_ui })
+    }
+}
+
+/// A tab's interface: what its document asked to hide, and what is hidden now.
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
+pub struct TabInterface {
+    pub asked: HiddenInterface,
+    pub hidden: HiddenInterface,
+}
+
+impl TabInterface {
+    /// The interface a document opens with: what it asks to hide, unless the user's preference
+    /// is to open every document their own way.
+    pub fn opening(asked: HiddenInterface, ignore_document: bool) -> Self {
+        if ignore_document { Self::default() } else { Self { asked, hidden: asked } }
+    }
+
+    /// [`TOGGLE`]: show everything that is hidden; with nothing hidden, hide what the document
+    /// asked to hide, or everything when it asked for nothing. Returns whether it is now hidden.
+    pub fn toggle(&mut self) -> bool {
+        self.hidden = if self.hidden.any() {
+            HiddenInterface::NONE
+        } else if self.asked.any() {
+            self.asked
+        } else {
+            HiddenInterface::ALL
+        };
+        self.hidden.any()
+    }
+}
+
+/// `FitWindow` and `CenterWindow`, waiting for the document's first frame (the size of its page
+/// on screen is known only once it is laid out).
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct PendingWindow {
+    pub doc: pdfcraft_engine::DocId,
+    pub fit: bool,
+    pub center: bool,
+    /// Frames left to wait for the document to be laid out before giving up.
+    pub frames_left: u8,
+}
+
+/// What the window looks like now, as the windowing layer reports it (points).
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct WindowNow {
+    /// The window's content area.
+    pub inner: Vec2,
+    /// The window with its frame, where the windowing layer knows it.
+    pub outer: Option<Rect>,
+    pub monitor: Option<Vec2>,
+    /// The document area inside the window.
+    pub document_area: Vec2,
+    pub maximized: bool,
+    pub fullscreen: bool,
+}
+
+/// The first displayed page (or spread) as the view lays it out.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct PageNow {
+    /// Its width and height on screen at 100%, in points.
+    pub size: Vec2,
+    /// The space the view keeps around it (gutters, margins, the gap in a spread), in points.
+    pub margins: Vec2,
+    /// The view's set zoom (1.0 = 100%); `None` when the view fits the page to the window.
+    pub zoom: Option<f32>,
+}
+
+/// Smallest window the fit makes, so a tiny page doesn't leave a sliver of a window.
+const MIN_INNER: Vec2 = vec2(480.0, 360.0);
+/// Share of the monitor the fitted window may take, leaving room for the desktop's own bars.
+const MONITOR_SHARE: f32 = 0.9;
+
+/// The viewport commands for `FitWindow` / `CenterWindow`. None for a maximized or full-screen
+/// window (resizing it would fight the user's choice), or when the sizes are unusable.
+///
+/// `FitWindow` keeps the document area's height and makes the window as wide as the page needs
+/// at that height when the view fits the page to the window, and makes the document area the
+/// page's size on screen when the view has a set zoom; either way within the monitor.
+/// `CenterWindow` centres the window on the monitor when the window is on the monitor at the
+/// desktop's origin (the windowing layer reports the monitor's size but not where it is).
+pub fn window_commands(now: WindowNow, page: PageNow, fit: bool, center: bool) -> Vec<ViewportCommand> {
+    let mut out = Vec::new();
+    if now.maximized || now.fullscreen || !usable(now.inner) || !usable(now.document_area) {
+        return out;
+    }
+    let chrome = (now.inner - now.document_area).max(Vec2::ZERO);
+    let mut inner = now.inner;
+    let zoom_ok = page.zoom.is_none_or(|z| z.is_finite() && z > 0.0);
+    if fit && zoom_ok && usable(page.size) && page.margins.x.is_finite() && page.margins.y.is_finite() {
+        let area = match page.zoom {
+            // Fitted to the window: keep the document area's height, and make the area as wide
+            // as the page is at the zoom that height gives it.
+            None => {
+                let zoom = ((now.document_area.y - page.margins.y) / page.size.y).max(0.0);
+                vec2(page.size.x * zoom + page.margins.x, now.document_area.y)
+            }
+            Some(zoom) => page.size * zoom + page.margins,
+        };
+        let mut target = area + chrome;
+        if let Some(monitor) = now.monitor.filter(|m| usable(*m)) {
+            target = target.min(monitor * MONITOR_SHARE);
+        }
+        target = target.max(MIN_INNER).round();
+        if usable(target) && (target - now.inner).length() >= 1.0 {
+            out.push(ViewportCommand::InnerSize(target));
+            inner = target;
+        }
+    }
+    if center
+        && let (Some(outer), Some(monitor)) = (now.outer, now.monitor.filter(|m| usable(*m)))
+        && Rect::from_min_size(Pos2::ZERO, monitor).contains(outer.min)
+    {
+        // The frame around the content area stays the size it is.
+        let frame = (outer.size() - now.inner).max(Vec2::ZERO);
+        let size = inner + frame;
+        let at = ((monitor - size) / 2.0).max(Vec2::ZERO).round();
+        if at.x.is_finite() && at.y.is_finite() && (at - outer.min.to_vec2()).length() >= 1.0 {
+            out.push(ViewportCommand::OuterPosition(at.to_pos2()));
+        }
+    }
+    out
+}
+
+fn usable(v: Vec2) -> bool {
+    v.x.is_finite() && v.y.is_finite() && v.x >= 1.0 && v.y >= 1.0
+}
+
+impl crate::PdfCraftApp {
+    /// The window and interface preferences of the document opening in tab `index`
+    /// ([`Self::apply_initial_view`] has applied its navigation, layout, zoom and page).
+    ///
+    /// - `HideToolbar`, `HideMenubar`, `HideWindowUI` hide those parts of the interface in its tab,
+    ///   unless Always use my default zoom and page layout is on, with a notice of the key that
+    ///   brings them back.
+    /// - A document that shows one page or one spread at a time (`/PageLayout /SinglePage`,
+    ///   `/TwoPageLeft`, `/TwoPageRight`) and names no zoom opens at fit page instead of the
+    ///   default zoom. ISO 32000-2 doesn't say which zoom such a layout opens at.
+    /// - `FitWindow`, `CenterWindow` wait for the page to be laid out
+    ///   ([`Self::window_preferences_frame`]), and only for the window's only document: a
+    ///   document opened in a tab beside others doesn't resize or move their window.
+    pub(crate) fn apply_viewer_preferences(&mut self, index: usize, v: &pdfcraft_engine::InitialView, activate: bool) {
+        use pdfcraft_engine::{InitialLayout as L, Magnification as M};
+        let own_view = self.always_default_view;
+        let only_document = self.views.len() == 1 && !self.combine_tab.open;
+        let Some(view) = self.views.get_mut(index) else { return };
+        view.interface = TabInterface::opening(HiddenInterface::asked_by(v), own_view);
+        if !own_view && v.magnification == M::Default && matches!(v.layout, L::SinglePage | L::TwoUp | L::TwoUpCoverPage) {
+            view.fit = crate::canvas::Fit::Page;
+        }
+        let (doc, hidden) = (view.id, view.interface.hidden.any());
+        if activate && hidden {
+            self.notify_interface_hidden();
+        }
+        // A browser page can't resize or move its window.
+        if !cfg!(target_arch = "wasm32") && activate && only_document && !self.full_screen && (v.fit_window || v.center_window) {
+            self.pending_window = Some(PendingWindow { doc, fit: v.fit_window, center: v.center_window, frames_left: 30 });
+        }
+    }
+
+    /// The parts of the interface hidden in the active tab.
+    pub fn hidden_interface(&self) -> HiddenInterface {
+        self.active.and_then(|i| self.views.get(i)).map_or(HiddenInterface::NONE, |v| v.interface.hidden)
+    }
+
+    /// [`TOGGLE`] in the active tab.
+    pub(crate) fn toggle_interface(&mut self) {
+        let Some(view) = self.active.and_then(|i| self.views.get_mut(i)) else { return };
+        if view.interface.toggle() {
+            self.notify_interface_hidden();
+        }
+    }
+
+    fn notify_interface_hidden(&mut self) {
+        let key = pdfcraft_engine::commands::command(TOGGLE).and_then(|c| c.shortcut).map(|s| s.label(cfg!(target_os = "macos"))).unwrap_or_default();
+        self.notify_fmt("This document hides the toolbars and panels. Press {key} to show them.", &[("key", &key)]);
+    }
+
+    /// `FitWindow` and `CenterWindow` for the document just opened, once its first page is laid
+    /// out. Dropped when another tab shows first, when another tab has opened behind it (it is no
+    /// longer the window's only document), or after a few frames without a layout.
+    pub(crate) fn window_preferences_frame(&mut self, ctx: &egui::Context) {
+        let Some(mut pending) = self.pending_window.take() else { return };
+        let Some((index, id)) = self.active_ids() else { return };
+        if id != pending.doc || self.views.len() != 1 || self.combine_tab.open {
+            return;
+        }
+        let Some(view) = self.views.get(index) else { return };
+        let area = view.viewport_rect();
+        let page = self.session.get(id).and_then(|d| view.first_page_now(&d.info));
+        let Some(page) = page.filter(|_| area.is_positive()) else {
+            if let Some(left) = pending.frames_left.checked_sub(1) {
+                pending.frames_left = left;
+                self.pending_window = Some(pending);
+                ctx.request_repaint();
+            }
+            return;
+        };
+        let content = ctx.content_rect().size();
+        let now = ctx.input(|i| {
+            let vp = i.viewport();
+            WindowNow {
+                inner: vp.inner_rect.map_or(content, |r| r.size()),
+                outer: vp.outer_rect,
+                monitor: vp.monitor_size,
+                document_area: area.size(),
+                maximized: vp.maximized.unwrap_or(false),
+                fullscreen: vp.fullscreen.unwrap_or(false),
+            }
+        });
+        for command in window_commands(now, page, pending.fit, pending.center) {
+            ctx.send_viewport_cmd(command);
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn now() -> WindowNow {
+        WindowNow {
+            inner: vec2(1400.0, 900.0),
+            outer: Some(Rect::from_min_size(Pos2::new(50.0, 40.0), vec2(1400.0, 930.0))),
+            monitor: Some(vec2(1920.0, 1080.0)),
+            document_area: vec2(1300.0, 800.0),
+            maximized: false,
+            fullscreen: false,
+        }
+    }
+
+    const FITTED: PageNow = PageNow { size: vec2(200.0, 300.0), margins: vec2(140.0, 56.0), zoom: None };
+
+    #[test]
+    fn a_fitted_page_gets_a_window_of_its_shape() {
+        // An 800-point-high area fits the 300-point page at 248%: 496 points wide plus margins,
+        // and the 100 points of interface beside the document area.
+        let c = window_commands(now(), FITTED, true, false);
+        assert_eq!(c, vec![ViewportCommand::InnerSize(vec2(736.0, 900.0))]);
+    }
+
+    #[test]
+    fn a_set_zoom_gets_the_page_size_within_the_monitor() {
+        let page = PageNow { size: vec2(400.0, 500.0), margins: vec2(100.0, 100.0), zoom: Some(1.0) };
+        assert_eq!(window_commands(now(), page, true, false), vec![ViewportCommand::InnerSize(vec2(600.0, 700.0))]);
+        // Too tall for the monitor: the window stops at the share of the monitor it may take.
+        let page = PageNow { size: vec2(1000.0, 2000.0), margins: Vec2::ZERO, zoom: Some(1.0) };
+        assert_eq!(window_commands(now(), page, true, false), vec![ViewportCommand::InnerSize(vec2(1100.0, 972.0))]);
+        // A tiny page doesn't make a sliver of a window.
+        let page = PageNow { size: vec2(10.0, 10.0), margins: Vec2::ZERO, zoom: Some(1.0) };
+        assert_eq!(window_commands(now(), page, true, false), vec![ViewportCommand::InnerSize(MIN_INNER)]);
+    }
+
+    #[test]
+    fn a_maximized_or_full_screen_window_is_left_alone() {
+        assert!(window_commands(WindowNow { maximized: true, ..now() }, FITTED, true, true).is_empty());
+        assert!(window_commands(WindowNow { fullscreen: true, ..now() }, FITTED, true, true).is_empty());
+        // Nothing asked, nothing done.
+        assert!(window_commands(now(), FITTED, false, false).is_empty());
+    }
+
+    #[test]
+    fn centring_uses_the_new_size_and_the_frame() {
+        let c = window_commands(now(), FITTED, true, true);
+        // 736 wide and 900 + 30 of frame high, on 1920 × 1080.
+        assert_eq!(c.get(1), Some(&ViewportCommand::OuterPosition(Pos2::new(592.0, 75.0))));
+        // Centre alone keeps the size.
+        let c = window_commands(now(), FITTED, false, true);
+        assert_eq!(c, vec![ViewportCommand::OuterPosition(Pos2::new(260.0, 75.0))]);
+        // A window on another monitor (outside the one at the origin) isn't moved.
+        let away = WindowNow { outer: Some(Rect::from_min_size(Pos2::new(2000.0, 40.0), vec2(1400.0, 930.0))), ..now() };
+        assert!(window_commands(away, FITTED, false, true).is_empty());
+        // Nor is one whose monitor or frame is unknown.
+        assert!(window_commands(WindowNow { monitor: None, ..now() }, FITTED, false, true).is_empty());
+        assert!(window_commands(WindowNow { outer: None, ..now() }, FITTED, false, true).is_empty());
+    }
+
+    #[test]
+    fn unusable_sizes_do_nothing() {
+        for bad in [Vec2::ZERO, vec2(f32::NAN, 10.0), vec2(f32::INFINITY, 10.0), vec2(-5.0, 10.0)] {
+            let page = PageNow { size: bad, ..FITTED };
+            assert!(window_commands(now(), page, true, false).is_empty(), "{bad:?}");
+            assert!(window_commands(WindowNow { inner: bad, ..now() }, FITTED, true, true).is_empty(), "{bad:?}");
+            assert!(window_commands(WindowNow { document_area: bad, ..now() }, FITTED, true, true).is_empty(), "{bad:?}");
+            assert!(window_commands(WindowNow { monitor: Some(bad), ..now() }, FITTED, false, true).is_empty(), "{bad:?}");
+        }
+        for zoom in [f32::NAN, 0.0, -1.0, f32::INFINITY] {
+            assert!(window_commands(now(), PageNow { zoom: Some(zoom), ..FITTED }, true, false).is_empty(), "{zoom}");
+        }
+        let page = PageNow { margins: vec2(f32::NAN, 0.0), ..FITTED };
+        assert!(window_commands(now(), page, true, false).is_empty());
+    }
+
+    #[test]
+    fn toggling_restores_and_rehides() {
+        let asked = HiddenInterface { toolbar: true, ..HiddenInterface::NONE };
+        let mut tab = TabInterface::opening(asked, false);
+        assert_eq!(tab.hidden, asked);
+        assert!(!tab.toggle());
+        assert_eq!(tab.hidden, HiddenInterface::NONE);
+        assert!(tab.toggle());
+        assert_eq!(tab.hidden, asked);
+        // The user's preference to open documents their own way hides nothing.
+        let mut own = TabInterface::opening(asked, true);
+        assert_eq!(own.hidden, HiddenInterface::NONE);
+        // A tab whose document asked for nothing hides everything, and shows it again.
+        assert!(own.toggle());
+        assert_eq!(own.hidden, HiddenInterface::ALL);
+        assert!(!own.toggle());
+    }
+
+    #[test]
+    fn the_mode_bar_goes_when_nothing_is_left_on_it() {
+        let toolbar = HiddenInterface { toolbar: true, ..HiddenInterface::NONE };
+        // The in-window menus are still there.
+        assert!(!toolbar.mode_bar(false));
+        // #4378 review: on macOS the native menu bar has the menus, so hiding the tools leaves an
+        // empty bar, which goes too.
+        assert!(toolbar.mode_bar(true));
+        let both = HiddenInterface { menubar: true, ..toolbar };
+        assert!(both.mode_bar(false) && both.mode_bar(true));
+        // Menus hidden, tools shown: the bar has the tools.
+        let menubar = HiddenInterface { menubar: true, ..HiddenInterface::NONE };
+        assert!(!menubar.mode_bar(false) && !menubar.mode_bar(true));
+    }
+}
diff --git a/crates/ui-egui/tests/it/main.rs b/crates/ui-egui/tests/it/main.rs
index 11b93089c4..f70f808d8a 100644
--- a/crates/ui-egui/tests/it/main.rs
+++ b/crates/ui-egui/tests/it/main.rs
@@ -92,4 +92,5 @@ mod ui;
 mod updates;
 mod view;
 mod viewer;
+mod viewer_prefs;
 mod xfa;
diff --git a/crates/ui-egui/tests/it/viewer_prefs.rs b/crates/ui-egui/tests/it/viewer_prefs.rs
new file mode 100644
index 0000000000..781e461668
--- /dev/null
+++ b/crates/ui-egui/tests/it/viewer_prefs.rs
@@ -0,0 +1,335 @@
+//! Viewer preferences applied when a document opens (ISO 32000-2 §12.2, Table 147): hiding the
+//! toolbars, menu and window controls in its tab, with F8 to bring them back; fitting and
+//! centring the window; and the zoom a one-page-at-a-time layout opens at.
+
+use egui_kittest::Harness;
+use egui_kittest::kittest::Queryable;
+use pdfcraft_ui_egui::PdfCraftApp;
+use pdfcraft_ui_egui::canvas::Fit;
+use pdfcraft_ui_egui::viewer_prefs::HiddenInterface;
+
+/// Two 200 × 300 pages; `catalog` is added to the catalog dictionary.
+fn fixture(catalog: &str) -> Vec<u8> {
+    let objs = [
+        format!("<< /Type /Catalog /Pages 2 0 R {catalog} >>"),
+        "<< /Type /Pages /Kids [3 0 R 4 0 R] /Count 2 /MediaBox [0 0 200 300] >>".into(),
+        "<< /Type /Page /Parent 2 0 R >>".into(),
+        "<< /Type /Page /Parent 2 0 R >>".into(),
+    ];
+    let mut out = b"%PDF-1.7\n".to_vec();
+    let mut offs = Vec::new();
+    for (i, o) in objs.iter().enumerate() {
+        offs.push(out.len());
+        out.extend_from_slice(format!("{} 0 obj\n{o}\nendobj\n", i + 1).as_bytes());
+    }
+    let x = out.len();
+    out.extend_from_slice(format!("xref\n0 {}\n0000000000 65535 f \n", objs.len() + 1).as_bytes());
+    for o in offs {
+        out.extend_from_slice(format!("{o:010} 00000 n \n").as_bytes());
+    }
+    out.extend_from_slice(format!("trailer\n<< /Size {} /Root 1 0 R >>\nstartxref\n{x}\n%%EOF\n", objs.len() + 1).as_bytes());
+    out
+}
+
+const HIDE_ALL: &str = "/ViewerPreferences << /HideToolbar true /HideMenubar true /HideWindowUI true >>";
+
+/// A plain document in the first tab and `files` after it, the last one active.
+fn harness(setup: impl FnOnce(&mut PdfCraftApp) + 'static, files: &'static [&'static str]) -> Harness<'static, PdfCraftApp> {
+    let mut h = Harness::builder().with_size(egui::vec2(1400.0, 900.0)).build_eframe(move |_cc| {
+        let mut app = PdfCraftApp::new();
+        app.set_option("language", "en").unwrap();
+        setup(&mut app);
+        for (i, catalog) in files.iter().enumerate() {
+            app.open_bytes(&format!("{i}.pdf"), None, fixture(catalog)).unwrap();
+        }
+        app
+    });
+    settle(&mut h);
+    h
+}
+
+fn settle(h: &mut Harness<'static, PdfCraftApp>) {
+    for _ in 0..3000 {
+        h.run_steps(2);
+        if !h.state().render_pending() {
+            break;
+        }
+        std::thread::sleep(std::time::Duration::from_millis(5));
+    }
+    h.run_steps(2);
+}
+
+/// Which of the toolbar (the command search), the menu (the menu bar's File menu) and the window
+/// controls (the rail's fit button) are on screen.
+fn shown(h: &Harness<'static, PdfCraftApp>) -> (bool, bool, bool) {
+    (
+        h.query_by_label("Find tools and commands").is_some(),
+        h.query_by(|n| n.role() == egui::accesskit::Role::MenuItem && n.label().as_deref() == Some("File")).is_some(),
+        h.query_by_label("Toggle fit page / fit width").is_some(),
+    )
+}
+
+#[test]
+fn a_document_that_hides_the_interface_opens_without_it_and_f8_brings_it_back() {
+    let mut h = harness(|_| {}, &["", HIDE_ALL]);
+    assert_eq!(shown(&h), (false, false, false), "the toolbar, menu and rail are hidden");
+    assert_eq!(h.state().hidden_interface(), HiddenInterface::ALL);
+    // The quick-action bar is a toolbar too.
+    assert!(h.query_by_label_contains("Hand (H)").is_none());
+    // The tab strip stays: the tabs and Home are still there.
+    h.get_by_label("Home");
+
+    h.key_press(egui::Key::F8);
+    h.run_steps(3);
+    assert_eq!(shown(&h), (true, true, true), "F8 shows them");
+    h.get_by_label_contains("Hand (H)");
+    h.key_press(egui::Key::F8);
+    h.run_steps(3);
+    assert_eq!(shown(&h), (false, false, false), "and hides them again");
+
+    // Another tab, whose document asks for nothing, has the usual interface.
+    h.state_mut().active = Some(0);
+    h.run_steps(3);
+    assert_eq!(shown(&h), (true, true, true));
+    h.state_mut().active = Some(1);
+    h.run_steps(3);
+    assert_eq!(shown(&h), (false, false, false));
+
+    // The command (palette, menus, automation) does what F8 does.
+    assert!(h.state_mut().execute("view.toggle_interface"));
+    h.run_steps(3);
+    assert_eq!(shown(&h), (true, true, true));
+}
+
+/// Reloading a file changed on disk keeps the tab's interface: hidden stays hidden, and F8 still
+/// hides only what the document asked for.
+#[test]
+fn a_reloaded_document_keeps_its_interface() {
+    let mut h = harness(|_| {}, &["/ViewerPreferences << /HideToolbar true >>"]);
+    let reload = |h: &mut Harness<'static, PdfCraftApp>| {
+        let info = h.state().session.get(h.state().views[0].id).unwrap().info.clone();
+        h.state_mut().views[0].document_replaced(&info);
+        h.run_steps(3);
+    };
+    reload(&mut h);
+    assert_eq!(shown(&h), (false, true, true), "still hidden after the reload");
+    h.key_press(egui::Key::F8);
+    h.run_steps(3);
+    assert_eq!(shown(&h), (true, true, true));
+    reload(&mut h);
+    assert_eq!(shown(&h), (true, true, true), "still shown after the reload");
+    h.key_press(egui::Key::F8);
+    h.run_steps(3);
+    assert_eq!(shown(&h), (false, true, true), "F8 hides only what the document asked for");
+}
+
+#[test]
+fn each_preference_hides_its_own_part() {
+    let top = |h: &Harness<'static, PdfCraftApp>| h.state().views[0].viewport_rect().top();
+    let mut h = harness(|_| {}, &["/ViewerPreferences << /HideToolbar true >>"]);
+    assert_eq!(shown(&h), (false, true, true), "HideToolbar");
+    // Shown and hidden again, F8 hides only what the document asked for.
+    h.key_press(egui::Key::F8);
+    h.run_steps(3);
+    assert_eq!(shown(&h), (true, true, true));
+    h.key_press(egui::Key::F8);
+    h.run_steps(3);
+    assert_eq!(shown(&h), (false, true, true));
+    let h = harness(|_| {}, &["/ViewerPreferences << /HideMenubar true >>"]);
+    assert_eq!(shown(&h), (true, false, true), "HideMenubar");
+    let h = harness(|_| {}, &["/ViewerPreferences << /HideWindowUI true >>"]);
+    assert_eq!(shown(&h), (true, true, false), "HideWindowUI");
+    assert!(h.state().hidden_interface().window_ui);
+    // False is the default, and is nothing to hide.
+    let h = harness(|_| {}, &["/ViewerPreferences << /HideToolbar false /HideMenubar false /HideWindowUI false >>"]);
+    assert_eq!(shown(&h), (true, true, true));
+    let with_bar = top(&h);
+    // With both the tools and the menu hidden, the mode bar goes and the document moves up.
+    let h = harness(|_| {}, &["/ViewerPreferences << /HideToolbar true /HideMenubar true >>"]);
+    assert_eq!(shown(&h), (false, false, true));
+    assert!(top(&h) < with_bar - 40.0, "{} against {with_bar}", top(&h));
+}
+
+#[test]
+fn hiding_the_window_controls_leaves_the_document_the_whole_width() {
+    // The document also asks for the page thumbnails panel, which is hidden with the rest.
+    let mut h = harness(|_| {}, &["/PageMode /UseThumbs /ViewerPreferences << /HideWindowUI true >>"]);
+    let width = |h: &Harness<'static, PdfCraftApp>| h.state().views[0].viewport_rect().width();
+    assert!(width(&h) > 1390.0, "{}", width(&h));
+    h.key_press(egui::Key::F8);
+    settle(&mut h);
+    // The rail and the Pages panel are back beside the document.
+    assert!(width(&h) < 1400.0 - 48.0 - 200.0, "{}", width(&h));
+}
+
+#[test]
+fn the_preference_to_ignore_document_views_keeps_the_interface() {
+    let h = harness(|app| app.always_default_view = true, &[HIDE_ALL]);
+    assert_eq!(shown(&h), (true, true, true));
+    assert_eq!(h.state().hidden_interface(), HiddenInterface::NONE);
+}
+
+#[test]
+fn f8_hides_the_interface_of_any_document_and_shows_it_again() {
+    let mut h = harness(|_| {}, &[""]);
+    assert_eq!(shown(&h), (true, true, true));
+    h.key_press(egui::Key::F8);
+    h.run_steps(3);
+    assert_eq!(shown(&h), (false, false, false));
+    h.get_by_label_contains("Press F8 to show them");
+    h.key_press(egui::Key::F8);
+    h.run_steps(3);
+    assert_eq!(shown(&h), (true, true, true));
+}
+
+#[test]
+fn hiding_the_interface_is_never_saved() {
+    let h = harness(|_| {}, &[HIDE_ALL]);
+    let settings = h.state().persist();
+    assert!(!settings.contains("interface"), "{settings}");
+}
+
+/// The fit a document with `catalog` opens at, with the user's defaults (fit width).
+fn opening_fit(catalog: &str, own_view: bool) -> Fit {
+    let mut app = PdfCraftApp::new();
+    app.always_default_view = own_view;
+    app.open_bytes("x.pdf", None, fixture(catalog)).unwrap();
+    app.views[0].fit
+}
+
+#[test]
+fn one_page_at_a_time_opens_at_fit_page() {
+    let default = opening_fit("", false);
+    assert_eq!(default, Fit::Width, "the default zoom");
+    for layout in ["SinglePage", "TwoPageLeft", "TwoPageRight"] {
+        assert_eq!(opening_fit(&format!("/PageLayout /{layout}"), false), Fit::Page, "{layout}");
+        // The user's preference keeps their zoom.
+        assert_eq!(opening_fit(&format!("/PageLayout /{layout}"), true), default, "{layout}");
+    }
+    // Scrolling layouts keep the default zoom.
+    for layout in ["OneColumn", "TwoColumnLeft", "TwoColumnRight"] {
+        assert_eq!(opening_fit(&format!("/PageLayout /{layout}"), false), default, "{layout}");
+    }
+    // A zoom the document names wins.
+    assert_eq!(opening_fit("/PageLayout /SinglePage /OpenAction [3 0 R /FitH 300]", false), Fit::Width);
+    let mut app = PdfCraftApp::new();
+    app.open_bytes("x.pdf", None, fixture("/PageLayout /SinglePage /OpenAction [3 0 R /XYZ 0 300 2]")).unwrap();
+    assert_eq!((app.views[0].fit, app.views[0].zoom), (Fit::None, 2.0));
+}
+
+/// Review on #4378: where the reader left off wins over the fit page a one-page-at-a-time
+/// layout opens at.
+#[test]
+fn a_remembered_zoom_wins_over_the_layouts_fit_page() {
+    let path = std::env::temp_dir().join(format!("pdfcraft-viewer-prefs-last-view-{}.pdf", std::process::id())).to_string_lossy().into_owned();
+    let mut app = PdfCraftApp::new();
+    let json_path = serde_json::to_string(&path).unwrap();
+    app.restore(&format!(r#"{{"last_views": [{{"path": {json_path}, "page": 1, "zoom": "62.5%", "display": "single"}}]}}"#));
+    assert!(app.restore_last_view);
+    app.open_bytes("x.pdf", Some(path), fixture("/PageLayout /SinglePage")).unwrap();
+    let v = &app.views[0];
+    assert_eq!((v.fit, v.zoom, v.current), (Fit::None, 0.625, 1));
+}
+
+/// The last `InnerSize` and `OuterPosition` asked for over `frames` frames.
+fn window_commands(h: &mut Harness<'static, PdfCraftApp>, frames: usize) -> (Option<egui::Vec2>, Option<egui::Pos2>) {
+    let (mut size, mut at) = (None, None);
+    for _ in 0..frames {
+        h.run_steps(1);
+        for c in &h.output().viewport_output[&egui::ViewportId::ROOT].commands {
+            match c {
+                egui::ViewportCommand::InnerSize(s) => size = Some(*s),
+                egui::ViewportCommand::OuterPosition(p) => at = Some(*p),
+                _ => {}
+            }
+        }
+    }
+    (size, at)
+}
+
+fn on_monitor(h: &mut Harness<'static, PdfCraftApp>) {
+    let vp = h.input_mut().viewports.entry(egui::ViewportId::ROOT).or_default();
+    vp.monitor_size = Some(egui::vec2(1920.0, 1080.0));
+    vp.inner_rect = Some(egui::Rect::from_min_size(egui::pos2(50.0, 70.0), egui::vec2(1400.0, 900.0)));
+    vp.outer_rect = Some(egui::Rect::from_min_size(egui::pos2(50.0, 40.0), egui::vec2(1400.0, 930.0)));
+}
+
+/// A harness whose window is on a 1920 × 1080 monitor, with one document opened in the first
+/// frames.
+fn windowed(files: &'static [&'static str]) -> Harness<'static, PdfCraftApp> {
+    let mut h = Harness::builder().with_size(egui::vec2(1400.0, 900.0)).build_eframe(|_cc| {
+        let mut app = PdfCraftApp::new();
+        app.set_option("language", "en").unwrap();
+        app
+    });
+    on_monitor(&mut h);
+    h.run_steps(2);
+    for (i, catalog) in files.iter().enumerate() {
+        h.state_mut().open_bytes(&format!("{i}.pdf"), None, fixture(catalog)).unwrap();
+    }
+    h
+}
+
+#[test]
+fn fit_window_sizes_the_window_to_the_first_page() {
+    let mut h = windowed(&["/ViewerPreferences << /FitWindow true >> /OpenAction [3 0 R /Fit]"]);
+    let (size, at) = window_commands(&mut h, 12);
+    let size = size.expect("the window is resized");
+    assert_eq!(at, None, "not moved");
+    // A 2:3 portrait page fitted to the window's height makes a narrower window.
+    assert!(size.x < 1000.0 && (size.y - 900.0).abs() < 1.0, "{size:?}");
+    // Asked once.
+    assert_eq!(window_commands(&mut h, 6), (None, None));
+    // The page now fills the document area's height and nearly its width.
+    let v = &h.state().views[0];
+    let (page, area) = (v.page_screen_rect(0).expect("shown"), v.viewport_rect());
+    assert!(area.width() - page.width() < 160.0, "page {page:?} in {area:?}");
+}
+
+#[test]
+fn center_window_centres_the_window_on_the_monitor() {
+    let mut h = windowed(&["/ViewerPreferences << /CenterWindow true >>"]);
+    // 1400 × 930 on 1920 × 1080.
+    assert_eq!(window_commands(&mut h, 12), (None, Some(egui::pos2(260.0, 75.0))));
+    let mut h = windowed(&["/ViewerPreferences << /FitWindow true /CenterWindow true >>"]);
+    let (size, at) = window_commands(&mut h, 12);
+    let (size, at) = (size.expect("resized"), at.expect("moved"));
+    assert!(((1920.0 - size.x) / 2.0 - at.x).abs() <= 0.5, "{size:?} at {at:?}");
+}
+
+#[test]
+fn a_maximized_window_or_a_second_tab_is_left_alone() {
+    let mut h = Harness::builder().with_size(egui::vec2(1400.0, 900.0)).build_eframe(|_cc| PdfCraftApp::new());
+    on_monitor(&mut h);
+    h.input_mut().viewports.entry(egui::ViewportId::ROOT).or_default().maximized = Some(true);
+    h.run_steps(2);
+    h.state_mut().open_bytes("0.pdf", None, fixture("/ViewerPreferences << /FitWindow true /CenterWindow true >>")).unwrap();
+    assert_eq!(window_commands(&mut h, 12), (None, None), "maximized");
+
+    let mut h = windowed(&["", "/ViewerPreferences << /FitWindow true /CenterWindow true >>"]);
+    assert_eq!(window_commands(&mut h, 12), (None, None), "beside another document");
+
+    // A tab opened behind the document before its page is laid out (a late startup file) leaves
+    // the window alone too, though the document stays active.
+    let mut h = windowed(&["/ViewerPreferences << /FitWindow true /CenterWindow true >>"]);
+    h.state_mut().open_bytes("1.pdf", None, fixture("")).unwrap();
+    h.state_mut().active = Some(0);
+    assert_eq!(window_commands(&mut h, 12), (None, None), "a tab opened behind it");
+}
+
+#[test]
+fn the_user_is_told_which_key_brings_the_interface_back() {
+    let mut h = windowed(&[HIDE_ALL]);
+    h.run_steps(3);
+    h.get_by_label_contains("This document hides the toolbars and panels. Press F8 to show them.");
+    // Not when nothing is hidden.
+    let mut h = windowed(&["/ViewerPreferences << /HideToolbar false /HideMenubar false /HideWindowUI false >>"]);
+    h.run_steps(3);
+    assert!(h.query_by_label_contains("Press F8").is_none());
+    // Nor when the user opens documents their own way.
+    let mut h = windowed(&[]);
+    h.state_mut().always_default_view = true;
+    h.state_mut().open_bytes("0.pdf", None, fixture(HIDE_ALL)).unwrap();
+    h.run_steps(3);
+    assert!(h.query_by_label_contains("Press F8").is_none());
+}
diff --git a/parity/acrobat-features.toml b/parity/acrobat-features.toml
index ebd7519ff8..072eac9eea 100644
--- a/parity/acrobat-features.toml
+++ b/parity/acrobat-features.toml
@@ -3584,10 +3584,10 @@ area = "D"
 tier = "P1"
 milestone = "M4"
 status = "shipped"
-commands = ["file.properties"]
+commands = ["file.properties", "view.toggle_interface"]
 tools = ["doc_initial_view"]
-evidence = ["crates/organize/src/view.rs::initial_view_resolves_indirect_boolean_preferences", "crates/ui-egui/tests/it/ui.rs::a_document_asking_for_full_screen_is_asked_about_first", "crates/organize/src/tests.rs::initial_view_round_trips_and_keeps_scripts", "crates/ui-egui/tests/it/viewer.rs::initial_view_is_edited_and_honoured_on_open", "crates/ui-egui/tests/it/viewer.rs::initial_view_magnification_offers_25_and_100_percent", "crates/organize/src/tests.rs::choosing_100_percent_keeps_an_actual_size_opening_destination", "crates/automation/tests/it/automation.rs::initial_view_through_tools", "crates/render/src/inspect/navigation.rs::a_go_to_action_opens_at_its_destination_explicit_or_named", "crates/ui-egui/tests/it/open_action.rs::an_xyz_open_action_puts_its_point_at_the_window_top_left", "crates/ui-egui/tests/it/open_action.rs::a_fith_open_action_puts_its_top_at_the_window_top", "crates/ui-egui/tests/it/open_action.rs::a_named_open_destination_opens_its_page", "crates/ui-egui/tests/it/open_action.rs::a_full_screen_document_shows_its_non_full_screen_panel_outside_full_screen", "crates/organize/src/tests.rs::an_unchanged_opening_destination_keeps_its_position_and_name", "crates/automation/tests/it/automation.rs::doc_info_reports_the_open_destination", "crates/organize/src/tests.rs::choosing_page_one_replaces_a_named_opening_destination", "crates/organize/src/tests.rs::a_named_opening_destination_is_kept_while_it_still_holds"]
-notes = "navigation panel, layout, magnification, page, window and interface options; honoured on open; script open actions kept. Open in Full Screen mode (/PageMode /FullScreen) asks first (Full Screen / Not now), as Acrobat does, instead of taking the screen. Window and interface options also read indirect boolean ViewerPreferences values. Missing: Acrobat's Full Screen preference to turn that alert off and its \"remember my choice for this document\" (misc.prefs-full-screen). On open the /OpenAction destination places the view as ISO 32000-2 Table 149 says (the /XYZ point at the window's top-left, /FitH and /FitV top or left at the edge), and a named destination (name or string, /Names /Dests tree or catalog /Dests, §12.3.2.4) resolves; Always use my default zoom keeps only the page. A full-screen document shows its /NonFullScreenPageMode panel outside full screen (Table 147). doc_info reports the opening destination. Document Properties keeps an opening action whose page and magnification are left alone, but still edits only those two; it shows a named destination's page and magnification, and choosing another page or magnification replaces the name with an explicit destination, except that page 1 at the default magnification removes /OpenAction so the first page opens. A name that resolves nowhere reads as page 1 and is kept until another page is chosen"
+evidence = ["crates/organize/src/view.rs::initial_view_resolves_indirect_boolean_preferences", "crates/ui-egui/tests/it/ui.rs::a_document_asking_for_full_screen_is_asked_about_first", "crates/organize/src/tests.rs::initial_view_round_trips_and_keeps_scripts", "crates/ui-egui/tests/it/viewer.rs::initial_view_is_edited_and_honoured_on_open", "crates/ui-egui/tests/it/viewer.rs::initial_view_magnification_offers_25_and_100_percent", "crates/organize/src/tests.rs::choosing_100_percent_keeps_an_actual_size_opening_destination", "crates/automation/tests/it/automation.rs::initial_view_through_tools", "crates/render/src/inspect/navigation.rs::a_go_to_action_opens_at_its_destination_explicit_or_named", "crates/ui-egui/tests/it/open_action.rs::an_xyz_open_action_puts_its_point_at_the_window_top_left", "crates/ui-egui/tests/it/open_action.rs::a_fith_open_action_puts_its_top_at_the_window_top", "crates/ui-egui/tests/it/open_action.rs::a_named_open_destination_opens_its_page", "crates/ui-egui/tests/it/open_action.rs::a_full_screen_document_shows_its_non_full_screen_panel_outside_full_screen", "crates/organize/src/tests.rs::an_unchanged_opening_destination_keeps_its_position_and_name", "crates/automation/tests/it/automation.rs::doc_info_reports_the_open_destination", "crates/organize/src/tests.rs::choosing_page_one_replaces_a_named_opening_destination", "crates/organize/src/tests.rs::a_named_opening_destination_is_kept_while_it_still_holds", "crates/ui-egui/tests/it/viewer_prefs.rs::a_document_that_hides_the_interface_opens_without_it_and_f8_brings_it_back", "crates/ui-egui/tests/it/viewer_prefs.rs::one_page_at_a_time_opens_at_fit_page", "crates/ui-egui/tests/it/viewer_prefs.rs::fit_window_sizes_the_window_to_the_first_page"]
+notes = "navigation panel, layout, magnification, page, window and interface options; honoured on open; script open actions kept. Open in Full Screen mode (/PageMode /FullScreen) asks first (Full Screen / Not now), as Acrobat does, instead of taking the screen. Window and interface options also read indirect boolean ViewerPreferences values. Missing: Acrobat's Full Screen preference to turn that alert off and its \"remember my choice for this document\" (misc.prefs-full-screen). On open the /OpenAction destination places the view as ISO 32000-2 Table 149 says (the /XYZ point at the window's top-left, /FitH and /FitV top or left at the edge), and a named destination (name or string, /Names /Dests tree or catalog /Dests, §12.3.2.4) resolves; Always use my default zoom keeps only the page. A full-screen document shows its /NonFullScreenPageMode panel outside full screen (Table 147). doc_info reports the opening destination. Document Properties keeps an opening action whose page and magnification are left alone, but still edits only those two; it shows a named destination's page and magnification, and choosing another page or magnification replaces the name with an explicit destination, except that page 1 at the default magnification removes /OpenAction so the first page opens. A name that resolves nowhere reads as page 1 and is kept until another page is chosen. HideToolbar, HideMenubar and HideWindowUI are applied in the document's tab only (the mode bar's tools and quick-action bar, the menu bar, the rail, side panels and scroll bars; the tab strip stays), never saved, skipped with Always use my default zoom and page layout, and F8 (view.toggle_interface) brings them back. FitWindow and CenterWindow apply to the window's only document when the window is neither maximized nor full screen; centring needs the window on the monitor at the desktop origin, and Wayland and the browser ignore both. SinglePage, TwoPageLeft and TwoPageRight without a named zoom open at fit page"
 
 [[feature]]
 id = "organize.custom-properties"