diff --git a/crates/ui-egui/src/content_ui.rs b/crates/ui-egui/src/content_ui.rs
index d30a814d43..4578d0d9d8 100644
--- a/crates/ui-egui/src/content_ui.rs
+++ b/crates/ui-egui/src/content_ui.rs
@@ -530,6 +530,7 @@ pub(crate) fn after_refresh(view: &mut DocView, added: &[Added]) {
 /// committed (a click away, or Done), and whether Done finished adding text. Discard or Escape
 /// throws the draft away.
 pub(crate) fn editor(ctx: &egui::Context, view: &mut DocView, info: &DocInfo, added: &[Added]) -> (Option<Edit>, bool) {
+    let doc_id = view.id;
     let Some(page) = view.content.draft.as_ref().map(|d| d.page) else { return (None, false) };
     let Some(xf) = view.page_xform(page) else { return (None, false) };
     let zoom = xf.rect.width() / xf.pw.max(1.0);
@@ -611,7 +612,7 @@ pub(crate) fn editor(ctx: &egui::Context, view: &mut DocView, info: &DocInfo, ad
                 |ui: &egui::Ui, text: &dyn egui::TextBuffer, wrap: f32| aligned_galley(ui, text.as_str(), &style, &line_font, color, wrap);
             let before = t.text.clone();
             let input = input_id();
-            crate::edit_text_ui::forget_typing_before(ui.ctx(), input, &mut t.typing_from, &t.style.text);
+            crate::edit_text_ui::forget_typing_before(ui.ctx(), input, doc_id, &mut t.typing_from, &t.style.text);
             ui.horizontal_top(|ui| {
                 ui.spacing_mut().item_spacing.x = 4.0;
                 let output = egui::TextEdit::multiline(&mut t.text)
diff --git a/crates/ui-egui/src/edit_text_ui.rs b/crates/ui-egui/src/edit_text_ui.rs
index 53426d8757..12adb622fb 100644
--- a/crates/ui-egui/src/edit_text_ui.rs
+++ b/crates/ui-egui/src/edit_text_ui.rs
@@ -266,18 +266,22 @@ pub(crate) fn input_id() -> egui::Id {
 }
 
 /// The page text box `id` keeps its own Undo history, across every paragraph or box it has shown
-/// (they share the id). Once the page has `text` (the box opened on it, or formatting applied it),
-/// that history is cleared: Undo in the box takes back only what was typed since, and then reaches
-/// the document. Kept, it put back text from another paragraph, or the whole paragraph as it was
-/// before a format change, into a box showing the page as it is now.
-pub(crate) fn forget_typing_before(ctx: &egui::Context, id: egui::Id, from: &mut Option<String>, text: &str) {
-    if from.as_deref() == Some(text) {
+/// in every tab (they share the id). Once the page has `text` (the box opened on it, or formatting
+/// applied it), that history is cleared: Undo in the box takes back only what was typed since, and
+/// then reaches the document. Kept, it put back text from another paragraph, or the whole paragraph
+/// as it was before a format change, into a box showing the page as it is now. `from` is the box's
+/// own record of that; which document `doc` last used the history is kept beside it, since a box
+/// in another tab on the same text would otherwise take that document's typing with its Redo.
+pub(crate) fn forget_typing_before(ctx: &egui::Context, id: egui::Id, doc: pdfcraft_engine::DocId, from: &mut Option<String>, text: &str) {
+    let owner = id.with("typing-doc");
+    if from.as_deref() == Some(text) && ctx.data(|d| d.get_temp::<pdfcraft_engine::DocId>(owner)) == Some(doc) {
         return;
     }
     if let Some(mut state) = egui::TextEdit::load_state(ctx, id) {
         state.clear_undoer();
         egui::TextEdit::store_state(ctx, id, state);
     }
+    ctx.data_mut(|d| d.insert_temp(owner, doc));
     *from = Some(text.to_owned());
 }
 
@@ -1624,6 +1628,7 @@ fn editor_galley(ui: &egui::Ui, ed: &LineEditor, text: &str, scale: f32, width:
 
 /// The inline editor; returns the edit once the text is applied.
 pub(crate) fn overlay(ctx: &egui::Context, view: &mut DocView, info: &DocInfo) -> Option<Edit> {
+    let view_id = view.id;
     // Clicks outside the document (the Format text panel) keep the paragraph open.
     // Where the click that took the focus was: the pointer itself may be gone by then (a touch, a
     // pen lifted away).
@@ -1743,7 +1748,7 @@ pub(crate) fn overlay(ctx: &egui::Context, view: &mut DocView, info: &DocInfo) -
                 };
                 let before = ed.text.clone();
                 let input = input_id();
-                forget_typing_before(ui.ctx(), input, &mut ed.typing_from, &ed.original);
+                forget_typing_before(ui.ctx(), input, view_id, &mut ed.typing_from, &ed.original);
                 let output = egui::TextEdit::multiline(&mut ed.text)
                     .id(input)
                     .font(font.clone())
diff --git a/crates/ui-egui/tests/it/content.rs b/crates/ui-egui/tests/it/content.rs
index 1fd887bf5e..18e3144f83 100644
--- a/crates/ui-egui/tests/it/content.rs
+++ b/crates/ui-egui/tests/it/content.rs
@@ -1033,3 +1033,40 @@ fn redo_with_an_unchanged_box_open_redoes_the_document() {
     assert!(now.bold, "the waiting Redo was redone");
     assert!(h.state().views[0].content.draft.is_none(), "the box closed with the step");
 }
+
+/// Two copies of a document, the same added text open in each: the boxes share one Undo history,
+/// so typing taken back with Undo in one tab came back with Redo in the other.
+#[test]
+fn typing_in_one_tab_never_reaches_another_tabs_added_text() {
+    let mut h = harness();
+    h.state_mut().open_bytes("copy.pdf", None, include_bytes!("../data/form.pdf").to_vec()).unwrap();
+    h.run_steps(4);
+    let text = pdfcraft_engine::AddedText { rect: [40.0, 195.0, 240.0, 210.0], text: "Reviewed".into(), ..Default::default() };
+    let open_in = |h: &mut Harness<'static, PdfCraftApp>, tab: usize| {
+        h.state_mut().active = Some(tab);
+        h.run_steps(2);
+        assert!(h.state_mut().execute("edit.text"));
+        h.run_steps(3);
+        let r = h.state().views[tab].page_screen_rect(0).expect("on screen");
+        let k = r.width() / 300.0;
+        click(h, r.min + egui::vec2(45.0 * k, 195.0 * k));
+        assert_eq!(h.state().views[tab].content.draft.as_ref().and_then(|d| d.index), Some(0), "the editor opened on the text");
+    };
+    for tab in [0, 1] {
+        h.state_mut().active = Some(tab);
+        assert!(h.state_mut().apply_edit(pdfcraft_engine::Edit::AddText { page: 0, text: text.clone() }));
+    }
+    open_in(&mut h, 1);
+    open_in(&mut h, 0);
+    h.key_press_modifiers(egui::Modifiers::COMMAND, egui::Key::End);
+    h.event(egui::Event::Text(" secret".into()));
+    h.run_steps(2);
+    h.key_press_modifiers(egui::Modifiers::COMMAND, egui::Key::Z);
+    h.run_steps(3);
+    assert_eq!(h.state().views[0].content.draft.as_ref().map(|d| d.text.as_str()), Some("Reviewed"), "taken back");
+    h.state_mut().active = Some(1);
+    h.run_steps(3);
+    h.key_press_modifiers(egui::Modifiers::COMMAND | egui::Modifiers::SHIFT, egui::Key::Z);
+    h.run_steps(3);
+    assert_eq!(h.state().views[1].content.draft.as_ref().map(|d| d.text.as_str()), Some("Reviewed"), "the other tab's typing stays out");
+}
diff --git a/crates/ui-egui/tests/it/editing.rs b/crates/ui-egui/tests/it/editing.rs
index 55a77452fc..f68f997a16 100644
--- a/crates/ui-egui/tests/it/editing.rs
+++ b/crates/ui-egui/tests/it/editing.rs
@@ -6233,3 +6233,48 @@ fn redo_from_the_menu_puts_the_typing_back_in_the_box() {
     let doc = s.session.get(s.views[0].id).unwrap();
     assert_eq!((doc.can_redo(), doc.text_blocks(0)[0].base_font.as_str()), (Some("Edit text"), "Helvetica"), "the document's Redo still waits");
 }
+
+/// Two copies of a document, the same paragraph open in each. The paragraph boxes share one text
+/// box, and so one Undo history: a box opened on the same text as another tab's didn't clear it.
+/// Typing in one tab, taken back with Undo, then came back with Redo (the key or the menu) in the
+/// other tab.
+#[test]
+fn typing_in_one_tab_never_reaches_another_tabs_paragraph() {
+    let mut h = harness(1, |app| {
+        app.open_bytes("copy.pdf", None, fixture(1)).expect("the copy opens");
+    });
+    let open_in = |h: &mut Harness<'static, PdfCraftApp>, tab: usize| {
+        h.state_mut().active = Some(tab);
+        h.run_steps(2);
+        assert!(h.state_mut().execute("edit.edit_text"));
+        h.run_steps(2);
+        let r = h.state().views[tab].page_screen_rect(0).expect("on screen");
+        click_at(h, egui::pos2(r.left() + 40.0 / 200.0 * r.width(), r.top() + (300.0 - 158.0) / 300.0 * r.height()));
+        assert!(h.state().views[tab].line_editor.is_some(), "the paragraph opens for typing");
+    };
+    open_in(&mut h, 1);
+    let original = h.state().views[1].line_editor.as_ref().unwrap().text.clone();
+    open_in(&mut h, 0);
+    assert_eq!(h.state().views[0].line_editor.as_ref().unwrap().text, original, "the same paragraph");
+    h.key_press_modifiers(Modifiers::COMMAND, Key::End);
+    h.event(egui::Event::Text(" secret".into()));
+    h.run_steps(2);
+    h.key_press_modifiers(Modifiers::COMMAND, Key::Z);
+    h.run_steps(3);
+    assert_eq!(h.state().views[0].line_editor.as_ref().unwrap().text, original, "taken back");
+    // The copy, its paragraph still open: Redo there has nothing of its own to put back.
+    h.state_mut().active = Some(1);
+    h.run_steps(3);
+    h.key_press_modifiers(Modifiers::COMMAND | Modifiers::SHIFT, Key::Z);
+    h.run_steps(3);
+    let text = h.state().views[1].line_editor.as_ref().map(|ed| ed.text.clone());
+    assert!(!text.as_deref().unwrap_or_default().contains("secret"), "the other tab's typing came in: {text:?}");
+    // Nor through what the menu's Redo runs, which reads the box's history itself (the menu item
+    // is off here, as the copy's document has nothing to redo).
+    h.state_mut().redo();
+    h.run_steps(3);
+    let s = h.state();
+    let text = s.views[1].line_editor.as_ref().map(|ed| ed.text.clone());
+    assert!(!text.as_deref().unwrap_or_default().contains("secret"), "the other tab's typing came in from the menu: {text:?}");
+    assert_eq!(s.session.get(s.views[1].id).unwrap().text_blocks(0)[0].text, s.session.get(s.views[0].id).unwrap().text_blocks(0)[0].text);
+}