FIX: Cope with Matrix entry in field annotations (#2736)

Closes #2731

pypdf/_writer.py

@@ -906,6 +906,10 @@ def _update_field_annotation(
  "/Length": 0,
  }
  )
+ if AA.AP in anno:
+ for k, v in cast(DictionaryObject, anno[AA.AP]).get("/N", {}).items():
+ if k not in {"/BBox", "/Length", "/Subtype", "/Type", "/Filter"}:
+ dct[k] = v
 
  # Update Resources with font information if necessary
  if font_res is not None:

tests/test_writer.py

@@ -2286,3 +2286,17 @@ def test_field_box_upside_down():
  box = writer.pages[0]["/Annots"][13].get_object()["/AP"]["/N"]["/BBox"]
  assert box[2] > 0
  assert box[3] > 0
+
+
+@pytest.mark.enable_socket()
+def test_matrix_entry_in_field_annots():
+ """Cf #2731"""
+ url = "https:/user-attachments/files/16036514/template.pdf"
+ name = "iss2731.pdf"
+ writer = PdfWriter(BytesIO(get_data_from_url(url, name=name)))
+ writer.update_page_form_field_values(
+ writer.pages[0],
+ {"Stellenbezeichnung_1": "some filled in text"},
+ auto_regenerate=False,
+ )
+ assert "/Matrix" in writer.pages[0]["/Annots"][5].get_object()["/AP"]["/N"]