BUG: Fix merge of a cropped page

PyPDF2/_page.py

@@ -539,16 +539,21 @@ def _merge_page(
         page2content = page2.getContents()
         if page2content is not None:
             page2content = ContentStream(page2content, self.pdf)
+            if(page2.cropBox.getWidth()<page2.trimBox.getWidth() or
+               page2.cropBox.getHeight()<page2.trimBox.getHeight()):
+                rect = page2.cropBox
+            else:
+                rect = page2.trimBox
             page2content.operations.insert(
                 0,
                 (
                     map(
                         FloatObject,
                         [
-                            page2.trimbox.left,
-                            page2.trimbox.bottom,
-                            page2.trimbox.width,
-                            page2.trimbox.height,
+                            rect.left,
+                            rect.bottom,
+                            rect.width,
+                            rect.height,
                         ],
                     ),
                     "re",

tests/test_page.py

@@ -1,10 +1,11 @@
 import json
 import os
 from copy import deepcopy
+import io
 
 import pytest
 
-from PyPDF2 import PdfReader, Transformation
+from PyPDF2 import PdfReader, PdfWriter, Transformation
 from PyPDF2._page import PageObject
 from PyPDF2.constants import PageAttributes as PG
 from PyPDF2.generic import DictionaryObject, NameObject, RectangleObject
@@ -176,6 +177,21 @@ def test_page_rotation_non90():
         page.rotate_clockwise(91)
     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.page[1])  # crossed to ease test reading
+    b = deepcopy(p.page[2])
+    a.cropbox = RectangleObject([100, 100, 300, 200])
+    w = PdfWriter()
+    w.add_page(a)
+    w.add_page(b)
+    c = deepcopy(b)
+    c.mergePage(a)
+    w.add_page(c)
+    o = io.BytesIO()
+    w.write(o)
+
 
 def test_page_scale():
     op = Transformation()
@@ -185,3 +201,4 @@ def test_page_scale():
 
     assert op.scale(sx=2).ctm == (2, 0, 0, 2, 0, 0)
     assert op.scale(sy=3).ctm == (3, 0, 0, 3, 0, 0)
+