pdf

PDF Skill

When To Use

• Read or review PDF content where layout and visuals matter.
• Create PDFs programmatically with reliable formatting.
• Fill and validate interactive PDF forms.
• Validate final rendering before delivery.

Workflow

1. Prefer visual review: render PDF pages to PNGs and inspect them.
   • Use pdftoppm from the bundled runtime or system Poppler when available.
   • If unavailable, install Poppler or ask the user to review the output locally.
2. Use reportlab to generate PDFs when creating new documents.
3. Use pdfplumber or pypdf for text extraction and quick checks; do not rely on text extraction for layout fidelity.
4. After each meaningful update, re-render pages and verify alignment, spacing, and legibility.

Fill And Validate AcroForms

Visual review alone is not a correctness check for a fillable PDF. A page /Widget annotation can render a value from its appearance stream while the canonical /AcroForm/Fields tree is missing or contains a stale value.

1. Keep the result interactive by default; set flatten=True only when the user explicitly requests a completed, static form. Preserve the source PDF, and do not flatten a signed PDF without an explicit workflow decision.
2. Inspect both representations before filling: enumerate fields from reader.get_fields() and /Widget annotations from every page's /Annots, following /Parent and /Kids. If a widget and a canonical field have the same name but are distinct objects with no /Parent relationship, do not call reattach_fields() blindly: it can create a second top-level field with the same name. Report the ambiguity or produce a static result.
3. Recover genuinely orphaned widgets, fill all pages, and write the result with pypdf:

from pypdf import PdfReader, PdfWriter
from pypdf.generic import NameObject

reader = PdfReader(input_pdf)
writer = PdfWriter()
writer.clone_document_from_reader(reader)

# Restores widgets that are missing from /AcroForm/Fields.
writer.reattach_fields()
fields = writer.get_fields() or {}
missing = set(expected_values) - set(fields)
if missing:
    raise ValueError(f"Form fields not found after repair: {sorted(missing)}")

values_to_write = dict(expected_values)
if flatten:
    # Paint every existing value before removing every widget.
    values_to_write = {
        name: field.get("/V", "/Off" if field.get("/FT") == "/Btn" else "")
        for name, field in fields.items()
    }
    values_to_write.update(expected_values)

writer.update_page_form_field_values(
    None, values_to_write, auto_regenerate=False, flatten=flatten
)

if flatten:
    # pypdf's flatten=True paints appearances but does not remove widgets.
    writer.remove_annotations(subtypes="/Widget")
    writer.root_object.pop(NameObject("/AcroForm"), None)

with open(output_pdf, "wb") as stream:
    writer.write(stream)