diff --git a/web/app.js b/web/app.js
index 6b06e6aed76c4..949d1c4ad7671 100644
--- a/web/app.js
+++ b/web/app.js
@@ -1165,6 +1165,14 @@ const PDFViewerApplication = {
     this.pdfLinkService.setDocument(pdfDocument, baseDocumentUrl);
     this.pdfDocumentProperties.setDocument(pdfDocument, this.url);
 
+    const annotationStorage = pdfDocument.annotationStorage;
+    annotationStorage.onSetModified = function () {
+      window.addEventListener("beforeunload", beforeUnload);
+    };
+    annotationStorage.onResetModified = function () {
+      window.removeEventListener("beforeunload", beforeUnload);
+    };
+
     const pdfViewer = this.pdfViewer;
     pdfViewer.setDocument(pdfDocument);
     const { firstPagePromise, onePageRendered, pagesPromise } = pdfViewer;
@@ -2951,6 +2959,12 @@ function webViewerKeyDown(evt) {
   }
 }
 
+function beforeUnload(evt) {
+  evt.preventDefault();
+  evt.returnValue = "";
+  return false;
+}
+
 /**
  * Converts API PageLayout values to the format used by `PDFViewer`.
  * NOTE: This is supported to the extent that the viewer implements the
diff --git a/web/base_viewer.js b/web/base_viewer.js
index 385a2ffe0d230..e4dce389ce784 100644
--- a/web/base_viewer.js
+++ b/web/base_viewer.js
@@ -127,12 +127,6 @@ function isSameScale(oldScale, newScale) {
   return false;
 }
 
-function beforeUnload(evt) {
-  evt.preventDefault();
-  evt.returnValue = "";
-  return false;
-}
-
 /**
  * Simple viewer control to display PDF content/pages.
  * @implements {IRenderableView}
@@ -442,12 +436,6 @@ class BaseViewer {
     const firstPagePromise = pdfDocument.getPage(1);
 
     const annotationStorage = pdfDocument.annotationStorage;
-    annotationStorage.onSetModified = function () {
-      window.addEventListener("beforeunload", beforeUnload);
-    };
-    annotationStorage.onResetModified = function () {
-      window.removeEventListener("beforeunload", beforeUnload);
-    };
 
     this._pagesCapability.promise.then(() => {
       this.eventBus.dispatch("pagesloaded", {