diff --git a/welco/sources/mail/static/js/welco.viewer.js b/welco/sources/mail/static/js/welco.viewer.js
index 17e511d..a9eec36 100644
--- a/welco/sources/mail/static/js/welco.viewer.js
+++ b/welco/sources/mail/static/js/welco.viewer.js
@@ -1,3 +1,7 @@
 window.addEventListener('message', function(event) {
-  PDFViewerApplication.open(event.data);
+  if (typeof(PDFViewerApplication) !== 'undefined') {
+    PDFViewerApplication.open(event.data);
+  } else {
+    PDFView.open(event.data);
+  }
 }, false);