Create real PDF signature fields

formfyxer/pdf_wrangling.py

@@ -238,7 +238,11 @@ def from_pikefield(cls, pike_field: PikeField) -> "FormField":
         )
 
     def get_bbox(self) -> BoundingBoxF:
-        if self.type == FieldType.TEXT or self.type == FieldType.AREA:
+        if (
+            self.type == FieldType.TEXT
+            or self.type == FieldType.AREA
+            or self.type == FieldType.SIGNATURE
+        ):
             return (
                 self.x,
                 self.y,
@@ -340,6 +344,55 @@ def _create_only_fields(
     c.save()
 
 
+def _normalize_signature_fields(pdf: Pdf, signature_field_names: Iterable[str]) -> None:
+    """Convert ReportLab text fields into PDF signature fields.
+
+    ReportLab does not expose an AcroForm signature widget API, so
+    ``_create_only_fields`` creates signature placeholders as text fields. This
+    function changes those generated widgets to ``/FT /Sig`` before they are
+    copied into the destination PDF.
+    """
+    signature_names = {
+        str(field_name).strip()
+        for field_name in signature_field_names
+        if str(field_name).strip()
+    }
+    if not signature_names or not hasattr(pdf.Root, "AcroForm"):
+        return
+
+    converted = 0
+
+    def _normalize_object(obj: Any) -> bool:
+        nonlocal converted
+        if obj is None or not hasattr(obj, "get"):
+            return False
+        field_name = str(obj.get("/T", "") or "").strip()
+        if field_name not in signature_names:
+            return False
+        if str(obj.get("/FT", "")) != "/Sig":
+            converted += 1
+        obj["/FT"] = pikepdf.Name("/Sig")
+        for key in ("/V", "/DV", "/MaxLen", "/Q", "/DS", "/RV"):
+            if key in obj:
+                del obj[key]
+        return True
+
+    for field in pdf.Root.AcroForm.get("/Fields", []):
+        if _normalize_object(field):
+            continue
+        if hasattr(field, "Kids"):
+            for kid in field.Kids:
+                if _normalize_object(kid):
+                    kid["/FT"] = pikepdf.Name("/Sig")
+
+    if converted:
+        try:
+            existing_flags = int(pdf.Root.AcroForm.get("/SigFlags", 0) or 0)
+        except (TypeError, ValueError):
+            existing_flags = 0
+        pdf.Root.AcroForm["/SigFlags"] = existing_flags | 3
+
+
 def set_fields(
     in_file: Union[str, Path, BinaryIO],
     out_file: Union[str, Path, BinaryIO],
@@ -384,6 +437,7 @@ def set_fields(
     if not fields_per_page:
         # Nothing to do, lol
         return
+    fields_per_page = [list(page_fields) for page_fields in fields_per_page]
     in_pdf = Pdf.open(in_file, allow_overwriting_input=overwrite)
     if hasattr(in_pdf.Root, "AcroForm") and not overwrite:
         print("Not going to overwrite the existing AcroForm!")
@@ -392,6 +446,13 @@ def set_fields(
     io_obj = io.BytesIO()
     _create_only_fields(io_obj, fields_per_page)
     temp_pdf = Pdf.open(io_obj)
+    signature_field_names = [
+        field.name
+        for page_fields in fields_per_page
+        for field in page_fields
+        if field.type == FieldType.SIGNATURE
+    ]
+    _normalize_signature_fields(temp_pdf, signature_field_names)
 
     in_pdf = copy_pdf_fields(source_pdf=temp_pdf, destination_pdf=in_pdf)
     in_pdf.save(out_file)

formfyxer/tests/test_pdf_labeling_rules.py

@@ -8,6 +8,7 @@
 from reportlab.pdfgen import canvas
 
 from formfyxer.pdf_wrangling import (
+    FieldType,
     FormField,
     _clamp_rect_to_page,
     _estimate_page_anchor_transform,
@@ -134,6 +135,56 @@ def test_copy_pdf_fields_anchor_adjusts_rectangles(self, mock_get_transforms):
             source_path.unlink(missing_ok=True)
             destination_path.unlink(missing_ok=True)
 
+    def test_set_fields_writes_real_signature_fields(self):
+        with NamedTemporaryFile(suffix=".pdf", delete=False) as base_tmp:
+            base_path = Path(base_tmp.name)
+        with NamedTemporaryFile(suffix=".pdf", delete=False) as labeled_tmp:
+            labeled_path = Path(labeled_tmp.name)
+
+        try:
+            c = canvas.Canvas(str(base_path))
+            c.drawString(72, 720, "Signature")
+            c.save()
+
+            set_fields(
+                str(base_path),
+                str(labeled_path),
+                [
+                    [
+                        FormField(
+                            "users1_signature",
+                            FieldType.SIGNATURE,
+                            72,
+                            650,
+                            font_size=12,
+                            configs={"width": 140, "height": 24},
+                        ),
+                        FormField.make_textbox(
+                            "users1_name", (72, 610, 140, 20), 12
+                        ),
+                    ]
+                ],
+                overwrite=True,
+            )
+
+            with pikepdf.Pdf.open(str(labeled_path)) as pdf:
+                fields = {
+                    str(field.get("/T")): field for field in pdf.Root.AcroForm.Fields
+                }
+                self.assertEqual(str(fields["users1_signature"].get("/FT")), "/Sig")
+                self.assertNotIn("/V", fields["users1_signature"])
+                self.assertNotIn("/DV", fields["users1_signature"])
+                self.assertEqual(str(fields["users1_name"].get("/FT")), "/Tx")
+                self.assertEqual(int(pdf.Root.AcroForm.get("/SigFlags", 0)), 3)
+
+            loaded_fields = get_existing_pdf_fields(str(labeled_path))
+            self.assertEqual(loaded_fields[0][0].type, FieldType.SIGNATURE)
+            self.assertEqual(loaded_fields[0][0].configs["width"], 140.0)
+            self.assertEqual(loaded_fields[0][0].configs["height"], 24.0)
+        finally:
+            base_path.unlink(missing_ok=True)
+            labeled_path.unlink(missing_ok=True)
+
     def test_improve_names_with_preferred_names(self):
         fields = [[FormField.make_textbox("page_0_field_0", (100, 100, 120, 20), 12)]]
         textboxes = [

pyproject.toml

@@ -2,6 +2,33 @@
 requires = ["setuptools>=40.0.0", "pip"]
 build-backend = "setuptools.build_meta"
 
+[dependency-groups]
+dev = [
+    "boxdetect",
+    "eyecite",
+    "mypy",
+    "numpy",
+    "ocrmypdf",
+    "openai",
+    "opencv-python-headless",
+    "pandas",
+    "pandas-stubs",
+    "pdf2image",
+    "pdfminer.six",
+    "pikepdf",
+    "pytest",
+    "python-docx",
+    "python-dotenv",
+    "reportlab",
+    "requests",
+    "sigfig",
+    "textstat",
+    "tiktoken",
+    "transformers",
+    "types-PyYAML",
+    "types-requests",
+]
+
 [tool.black]
 extend-exclude = '(__init__.py|setup.py)'