fix(ocr): add page.flatten() for fillable PDFs without appearance streams (#240)

init_forms() alone is insufficient for fillable PDFs that lack pre-generated
appearance streams for form fields (common in government forms like VA-21-22a).
page.flatten() forces PDFium to generate appearances and merge them into page
content before rendering, ensuring all form field values are visible.

Changes:
- ocr/service.py: add page.flatten() before _extract_page_image() in rendering loop
- bda_processresults_function/index.py: add page.flatten() before render()
- test_ocr_service.py: verify both init_forms() and flatten() are called
- CHANGELOG.md: update fix description with two-part explanation

Author: Bob Strahan

CHANGELOG.md

@@ -38,7 +38,7 @@ SPDX-License-Identifier: MIT-0
 
 ### Fixed
 
-- **Fillable PDF form fields missing from rendered page images** — Fixed bug where fillable PDF form fields (text inputs, checkboxes, radio buttons, dropdowns) were not rendered in page images, causing OCR and extraction to miss user-entered data. Root cause: pypdfium2's `render(may_draw_forms=True)` requires `PdfDocument.init_forms()` to be called first to initialize the form rendering engine. Added `init_forms()` call in both Pattern 2 (`OcrService`) and Pattern 1 (`create_pdf_page_images`) PDF rendering pipelines. ([#240](https://github.com/aws-solutions-library-samples/accelerated-intelligent-document-processing-on-aws/issues/240))
+- **Fillable PDF form fields missing from rendered page images** — Fixed bug where fillable PDF form fields (text inputs, checkboxes, radio buttons, dropdowns) were not rendered in page images, causing OCR and extraction to miss user-entered data. Two-part fix: (1) `PdfDocument.init_forms()` initializes the form rendering engine so PDFium can process form fields, and (2) `page.flatten()` merges form field appearances into page content before rendering — required because many fillable PDFs (especially government forms) lack pre-generated appearance streams. Applied in both Pattern 2 (`OcrService`) and Pattern 1 (`create_pdf_page_images`) PDF rendering pipelines. ([#240](https://github.com/aws-solutions-library-samples/accelerated-intelligent-document-processing-on-aws/issues/240))
 
 - **Discovery subscription handler dropping errorMessage and other fields** — Fixed bug where the UI subscription handler did `{ ...oldJob, status: updatedJob.status }`, discarding all fields except status from real-time subscription updates. Error messages, discovered class names, and status messages were being sent by the backend but silently dropped by the UI. Now spreads all fields: `{ ...oldJob, ...updatedJob }`.
 

lib/idp_common_pkg/idp_common/ocr/service.py

@@ -426,6 +426,12 @@ def process_document(self, document: Document) -> Document:
                     page_images: Dict[int, bytes] = {}
                     for i in pages_to_render:
                         page = pdf_document[i]
+                        # Flatten form fields into page content before rendering.
+                        # Many fillable PDFs (e.g., government forms) lack appearance
+                        # streams for form fields — flatten() forces PDFium to generate
+                        # them and merge into page content so render() can display them.
+                        # Requires init_forms() to have been called before page retrieval.
+                        page.flatten()
                         page_images[i] = self._extract_page_image(page, True, i + 1)
 
                     pdf_document.close()

lib/idp_common_pkg/tests/unit/ocr/test_ocr_service.py

@@ -353,6 +353,11 @@ def test_process_document_calls_init_forms_for_fillable_pdfs(
             # Verify init_forms() was called to enable fillable PDF form rendering
             mock_pdf_doc.init_forms.assert_called_once()
 
+            # Verify flatten() was called on the page to merge form fields
+            # into page content (needed for PDFs without appearance streams)
+            mock_page = mock_pdf_doc.__getitem__.return_value
+            mock_page.flatten.assert_called_once()
+
     @patch("boto3.client")
     @patch("idp_common.ocr.service.pdfium.PdfDocument")
     def test_process_document_success(

patterns/unified/src/bda_processresults_function/index.py

@@ -165,6 +165,11 @@ def create_pdf_page_images(bda_result_bucket, output_bucket, object_key):
         for page_num in range(len(pdf_document)):
             # Render page to a PIL image
             page = pdf_document[page_num]
+            # Flatten form fields into page content before rendering.
+            # Many fillable PDFs (e.g., government forms) lack appearance
+            # streams for form fields — flatten() forces PDFium to generate
+            # them and merge into page content so render() can display them.
+            page.flatten()
             pil_img = page.render(scale=150 / 72).to_pil()
 
             # Save the image to a BytesIO object as JPEG