BUG: Cope with extra space (#2151)

Closes #1903

pypdf/_writer.py

@@ -862,6 +862,7 @@ def _update_text_field(self, field: DictionaryObject) -> None:
         # Extract font information
         da = cast(str, field[AA.DA])
         font_properties = da.replace("\n", " ").replace("\r", " ").split(" ")
+        font_properties = [x for x in font_properties if x != ""]
         font_name = font_properties[font_properties.index("Tf") - 2]
         font_height = float(font_properties[font_properties.index("Tf") - 1])
         if font_height == 0:

tests/test_writer.py

@@ -1788,6 +1788,20 @@ def test_viewerpreferences():
     assert writer.viewer_preferences is None
 
 
+def test_extra_spaces_in_da_text(caplog):
+    writer = PdfWriter(clone_from=RESOURCE_ROOT / "form.pdf")
+    t = writer.pages[0]["/Annots"][0].get_object()["/DA"]
+    t = t.replace("/Helv", "/Helv   ")
+    writer.pages[0]["/Annots"][0].get_object()[NameObject("/DA")] = TextStringObject(t)
+    writer.update_page_form_field_values(
+        writer.pages[0], {"foo": "abcd"}, auto_regenerate=False
+    )
+    t = writer.pages[0]["/Annots"][0].get_object()["/AP"]["/N"].get_data()
+    assert "Font dictionary for  not found." not in caplog.text
+    assert b"/Helv" in t
+    assert b"(abcd)" in t
+
+
 @pytest.mark.enable_socket()
 def test_object_contains_indirect_reference_to_self():
     url = "https://github.com/py-pdf/pypdf/files/12389243/testbook.pdf"