Update app.py

app.py

@@ -15,7 +15,10 @@ class MultiDocMerger:
     def add_document(self, file):
         file_path = os.path.join(self.temp_dir, file.name)
         with open(file_path, 'wb') as f:
-            f.write(file.read())
+            f.write(file.file.read())  # Use file.file.read() instead of file.read()
+        self.documents.append(file_path)
+        self._extract_pages(file_path)
+        return self._generate_preview()
         self.documents.append(file_path)
         self._extract_pages(file_path)
         return self._generate_preview()