diff --git a/backend/app/services/pdf_generator_service.py b/backend/app/services/pdf_generator_service.py
index 8fe1137..611114e 100644
--- a/backend/app/services/pdf_generator_service.py
+++ b/backend/app/services/pdf_generator_service.py
@@ -1064,17 +1064,39 @@ class PDFGeneratorService:
 
             # Step 4: Detect content orientation mismatch
             # This handles rotated scans where content bbox exceeds page dimensions
-            needs_rotation, adjusted_width, adjusted_height = self._detect_content_orientation(
-                target_width, target_height, ocr_data
+            # IMPORTANT: Use OCR dimensions (pixels) for detection, not PDF points
+            # because content bboxes are in the same coordinate system as OCR dimensions
+            needs_rotation, adjusted_ocr_width, adjusted_ocr_height = self._detect_content_orientation(
+                ocr_width, ocr_height, ocr_data
             )
 
+            # If orientation change detected, calculate the adjusted target dimensions
+            if needs_rotation:
+                # Swap target dimensions to match the detected orientation
+                adjusted_width = target_height
+                adjusted_height = target_width
+            elif adjusted_ocr_width != ocr_width or adjusted_ocr_height != ocr_height:
+                # Content extends beyond OCR dimensions, scale target proportionally
+                scale_w = adjusted_ocr_width / ocr_width if ocr_width > 0 else 1.0
+                scale_h = adjusted_ocr_height / ocr_height if ocr_height > 0 else 1.0
+                adjusted_width = target_width * scale_w
+                adjusted_height = target_height * scale_h
+            else:
+                adjusted_width = target_width
+                adjusted_height = target_height
+
             if needs_rotation or (adjusted_width != target_width or adjusted_height != target_height):
                 logger.info(f"頁面尺寸調整: {target_width:.1f}x{target_height:.1f} -> "
                            f"{adjusted_width:.1f}x{adjusted_height:.1f} (旋轉={needs_rotation})")
                 target_width, target_height = adjusted_width, adjusted_height
-                # Also update page_dimensions for consistency in per-page processing
+                # Update BOTH page_dimensions AND original_page_sizes for consistency
+                # This ensures per-page processing uses the adjusted dimensions
                 if 0 in page_dimensions:
                     page_dimensions[0] = {'width': target_width, 'height': target_height}
+                if 0 in original_page_sizes:
+                    # Override original file dimensions with content-based dimensions
+                    original_page_sizes[0] = (target_width, target_height)
+                    logger.info(f"覆蓋原始文件尺寸以適應內容方向")
 
             # Create PDF canvas with initial page size (will be updated per page)
             pdf_canvas = canvas.Canvas(str(output_path), pagesize=(target_width, target_height))