BUG: Fix merge of a cropped page

PyPDF2/_page.py

@@ -524,7 +524,13 @@ def _merge_page(
         page2content = page2.get_contents()
         if page2content is not None:
             page2content = ContentStream(page2content, self.pdf)
-            rect = page2.trimbox
+            if (
+                page2.cropbox.width < page2.trimbox.width
+                or page2.cropbox.height < page2.trimbox.height
+            ):
+                rect = page2.cropbox
+            else:
+                rect = page2.trimbox
             page2content.operations.insert(
                 0,
                 (

tests/test_page.py

@@ -1,6 +1,7 @@
 import json
 import os
 from copy import deepcopy
+import io
 from io import BytesIO
 from pathlib import Path
 
@@ -205,6 +206,21 @@ def test_page_rotation_non90():
     assert exc.value.args[0] == "Rotation angle must be a multiple of 90"
 
 
+def test_page_merge_cropped():
+    p = PdfReader(os.path.join(RESOURCE_ROOT, "issue-604.pdf"))
+    a = deepcopy(p.pages[1])  # crossed to ease test reading
+    b = deepcopy(p.pages[2])
+    a.cropbox = RectangleObject([100, 100, 300, 200])
+    w = PdfWriter()
+    w.add_page(a)
+    w.add_page(b)
+    c = deepcopy(b)
+    c.merge_page(a)
+    w.add_page(c)
+    o = io.BytesIO()
+    w.write(o)
+
+
 def test_page_scale():
     op = Transformation()
     with pytest.raises(ValueError) as exc: