diff --git a/cps/static/js/libs/pdf.mjs b/cps/static/js/libs/pdf.js
similarity index 99%
rename from cps/static/js/libs/pdf.mjs
rename to cps/static/js/libs/pdf.js
index 52a97c21..13face72 100644
--- a/cps/static/js/libs/pdf.mjs
+++ b/cps/static/js/libs/pdf.js
@@ -16667,7 +16667,7 @@ const PDFWorkerUtil = {
 {
   if (isNodeJS) {
     PDFWorkerUtil.isWorkerDisabled = true;
-    GlobalWorkerOptions.workerSrc ||= "./pdf.worker.mjs";
+    GlobalWorkerOptions.workerSrc ||= "./pdf.worker.js";
   }
   PDFWorkerUtil.isSameOrigin = function (baseUrl, otherUrl) {
     let base;
@@ -24745,4 +24745,4 @@ var __webpack_exports__shadow = __webpack_exports__.shadow;
 var __webpack_exports__version = __webpack_exports__.version;
 export { __webpack_exports__AbortException as AbortException, __webpack_exports__AnnotationEditorLayer as AnnotationEditorLayer, __webpack_exports__AnnotationEditorParamsType as AnnotationEditorParamsType, __webpack_exports__AnnotationEditorType as AnnotationEditorType, __webpack_exports__AnnotationEditorUIManager as AnnotationEditorUIManager, __webpack_exports__AnnotationLayer as AnnotationLayer, __webpack_exports__AnnotationMode as AnnotationMode, __webpack_exports__CMapCompressionType as CMapCompressionType, __webpack_exports__ColorPicker as ColorPicker, __webpack_exports__DOMSVGFactory as DOMSVGFactory, __webpack_exports__DrawLayer as DrawLayer, __webpack_exports__FeatureTest as FeatureTest, __webpack_exports__GlobalWorkerOptions as GlobalWorkerOptions, __webpack_exports__ImageKind as ImageKind, __webpack_exports__InvalidPDFException as InvalidPDFException, __webpack_exports__MissingPDFException as MissingPDFException, __webpack_exports__OPS as OPS, __webpack_exports__PDFDataRangeTransport as PDFDataRangeTransport, __webpack_exports__PDFDateString as PDFDateString, __webpack_exports__PDFWorker as PDFWorker, __webpack_exports__PasswordResponses as PasswordResponses, __webpack_exports__PermissionFlag as PermissionFlag, __webpack_exports__PixelsPerInch as PixelsPerInch, __webpack_exports__RenderingCancelledException as RenderingCancelledException, __webpack_exports__TextLayer as TextLayer, __webpack_exports__UnexpectedResponseException as UnexpectedResponseException, __webpack_exports__Util as Util, __webpack_exports__VerbosityLevel as VerbosityLevel, __webpack_exports__XfaLayer as XfaLayer, __webpack_exports__build as build, __webpack_exports__createValidAbsoluteUrl as createValidAbsoluteUrl, __webpack_exports__fetchData as fetchData, __webpack_exports__getDocument as getDocument, __webpack_exports__getFilenameFromUrl as getFilenameFromUrl, __webpack_exports__getPdfFilenameFromUrl as getPdfFilenameFromUrl, __webpack_exports__getXfaPageViewport as getXfaPageViewport, __webpack_exports__isDataScheme as isDataScheme, __webpack_exports__isPdfFile as isPdfFile, __webpack_exports__noContextMenu as noContextMenu, __webpack_exports__normalizeUnicode as normalizeUnicode, __webpack_exports__setLayerDimensions as setLayerDimensions, __webpack_exports__shadow as shadow, __webpack_exports__version as version };
 
-//# sourceMappingURL=pdf.mjs.map
\ No newline at end of file
+//# sourceMappingURL=pdf.mjs.map
diff --git a/cps/static/js/libs/pdf.worker.mjs b/cps/static/js/libs/pdf.worker.js
similarity index 100%
rename from cps/static/js/libs/pdf.worker.mjs
rename to cps/static/js/libs/pdf.worker.js
diff --git a/cps/static/js/libs/viewer.mjs b/cps/static/js/libs/viewer.js
similarity index 99%
rename from cps/static/js/libs/viewer.mjs
rename to cps/static/js/libs/viewer.js
index ba57b079..9f797c3b 100644
--- a/cps/static/js/libs/viewer.mjs
+++ b/cps/static/js/libs/viewer.js
@@ -828,7 +828,7 @@ const defaultOptions = {
     kind: OptionKind.WORKER
   },
   workerSrc: {
-    value: "../build/pdf.worker.mjs",
+    value: "../build/pdf.worker.js",
     kind: OptionKind.WORKER
   }
 };
diff --git a/cps/templates/readpdf.html b/cps/templates/readpdf.html
index c747d02e..6d9c3f07 100644
--- a/cps/templates/readpdf.html
+++ b/cps/templates/readpdf.html
@@ -35,7 +35,7 @@ See https://github.com/adobe-type-tools/cmap-resources
     <link rel="stylesheet" href="{{ url_for('static', filename='css/libs/viewer.css') }}">
 	  <!-- This snippet is used in production (included from viewer.html) -->
 	  <link rel="resource" type="application/l10n" href="{{ url_for('static', filename='locale/locale.json') }}">
-	  <script src="{{ url_for('static', filename='js/libs/pdf.mjs') }}" type="module"></script>
+	  <script src="{{ url_for('static', filename='js/libs/pdf.js') }}" type="module"></script>
 
     <script type="text/javascript">
     window.addEventListener('webviewerloaded', function() {
@@ -46,12 +46,12 @@ See https://github.com/adobe-type-tools/cmap-resources
         PDFViewerApplicationOptions.set('cMapUrl', "{{ url_for('static', filename='cmaps/') }}");
         PDFViewerApplicationOptions.set('sidebarViewOnLoad', 0);
         PDFViewerApplicationOptions.set('imageResourcesPath', "{{ url_for('static', filename='css/images/') }}");
-        PDFViewerApplicationOptions.set('workerSrc', "{{ url_for('static', filename='js/libs/pdf.worker.mjs') }}");
+        PDFViewerApplicationOptions.set('workerSrc', "{{ url_for('static', filename='js/libs/pdf.worker.js') }}");
         PDFViewerApplicationOptions.set('defaultUrl',"{{ url_for('web.serve_book', book_id=pdffile, book_format='pdf') }}")
     });
     </script>
 
-    <script src="{{ url_for('static', filename='js/libs/viewer.mjs') }}" type="module">></script>
+    <script src="{{ url_for('static', filename='js/libs/viewer.js') }}" type="module">></script>
 
   </head>