diff --git a/b0esche_cloud/lib/pages/document_viewer.dart b/b0esche_cloud/lib/pages/document_viewer.dart
index 05ab0d1..48b4700 100644
--- a/b0esche_cloud/lib/pages/document_viewer.dart
+++ b/b0esche_cloud/lib/pages/document_viewer.dart
@@ -457,15 +457,28 @@ class _DocumentViewerModalState extends State<DocumentViewerModal> {
   }
 
   Widget _buildCollaboraIframe(String collaboraUrl) {
-    // For Collabora Online, create an iframe that loads the editor directly
-    const String viewType = 'collabora-iframe';
+    // For Collabora Online, we need to POST the WOPISrc, not GET it
+    // Create an iframe and submit a form to load the document
+    const String viewType = 'collabora-form';
     
     ui.platformViewRegistry.registerViewFactory(
       viewType,
       (int viewId) {
-        // Create the iframe with the properly encoded Collabora URL
+        // Extract the WOPISrc from the URL
+        final uri = Uri.parse(collaboraUrl);
+        final wopisrc = uri.queryParameters['WOPISrc'] ?? '';
+        
+        // Create a container for the form and iframe
+        final container = html.DivElement()
+          ..style.width = '100%'
+          ..style.height = '100%'
+          ..style.margin = '0'
+          ..style.padding = '0'
+          ..style.overflow = 'hidden';
+        
+        // Create the iframe first
         final iframe = html.IFrameElement()
-          ..src = collaboraUrl
+          ..name = 'collabora-iframe'
           ..style.border = 'none'
           ..style.width = '100%'
           ..style.height = '100%'
@@ -475,13 +488,35 @@ class _DocumentViewerModalState extends State<DocumentViewerModal> {
             'allow',
             'microphone; camera; usb; autoplay; clipboard-read; clipboard-write',
           )
-          // Remove allow-same-origin for security, add allow-popups-to-escape-sandbox
           ..setAttribute(
             'sandbox',
             'allow-scripts allow-popups allow-forms allow-pointer-lock allow-presentation allow-modals allow-downloads allow-popups-to-escape-sandbox',
           );
         
-        return iframe;
+        container.append(iframe);
+        
+        // Create a hidden form that will POST to Collabora
+        final form = html.FormElement()
+          ..method = 'POST'
+          ..action = 'https://of.b0esche.cloud/loleaflet/dist/loleaflet.html'
+          ..target = 'collabora-iframe'
+          ..style.display = 'none';
+        
+        // Add WOPISrc as a hidden input
+        final wopisrcInput = html.InputElement()
+          ..type = 'hidden'
+          ..name = 'WOPISrc'
+          ..value = wopisrc;
+        
+        form.append(wopisrcInput);
+        container.append(form);
+        
+        // Use a timer to submit the form after the iframe is fully loaded
+        Future.delayed(const Duration(milliseconds: 100), () {
+          form.submit();
+        });
+        
+        return container;
       },
     );