sigdetect 0.4.0

Signature detection and role attribution for PDFs

CaseWorks.Automation.CaseDocumentIntake

sigdetect

sigdetect is a small Python library + CLI that detects e-signature evidence in PDFs and infers the signer role (e.g., patient, attorney, representative).

It looks for:

• Real signature form fields (/Widget annotations with /FT /Sig)
• AcroForm signature fields present only at the document level
• Common vendor markers (e.g., DocuSign, “Signature Certificate”)
• Page labels (like “Signature of Patient” or “Signature of Parent/Guardian”)

It returns a structured summary per file (pages, counts, roles, hints, etc.) that can be used downstream.

---

Contents

• Quick start
• CLI usage
• Library usage
• Result schema
• Configuration & rules
• Smoke tests
• Dev workflow
• Troubleshooting
• License

---

Quick start

Requirements

• Python 3.9+ (developed & tested on 3.11)
• macOS / Linux / WSL

Setup

# 1) Create and activate a virtualenv (example uses Python 3.11)
python3.11 -m venv .venv
source .venv/bin/activate

# 2) Install in editable (dev) mode
python -m pip install --upgrade pip
pip install -e .

Sanity check

# Run unit & smoke tests
pytest -q

---

CLI usage

The project ships a Typer-based CLI (exposed either as sigdetect or runnable via python -m sigdetect.cli, depending on how it is installed).

sigdetect --help
# or
python -m sigdetect.cli --help

Detect (per-file summary)

# Execute detection according to the YAML configuration
sigdetect detect \
  --config ./sample_data/config.yml \
  --profile hipaa            # or: retainer

Notes

• The config file controls pdf_root, out_dir, engine, pseudo_signatures, recurse_xobjects, etc.
• --engine accepts auto (default; prefers PyMuPDF when installed, falls back to PyPDF2), pypdf2, or pymupdf.
• --pseudo-signatures enables a vendor/Acro-only pseudo-signature when no actual /Widget is present (useful for DocuSign / Acrobat Sign receipts).
• --recurse-xobjects allows scanning Form XObjects for vendor markers and labels embedded in page resources.
• --profile selects tuned role logic:
  • hipaa → patient / representative / attorney
  • retainer → client / firm (prefers detecting two signatures)
• --recursive/--no-recursive toggles whether sigdetect detect descends into subdirectories when hunting for PDFs (recursive by default).
• Cropping (--crop-signatures) and wet detection (--detect-wet) are enabled by default for single-pass runs; disable them if you want a light, e-sign-only pass. PyMuPDF is required for crops; PyMuPDF + Tesseract are required for wet detection.
• If the executable is not on PATH, you can always fall back to python -m sigdetect.cli ....

EDA (quick aggregate stats)

sigdetect eda \
  --config ./sample_data/config.yml

---

Library usage

from pathlib import Path
from sigdetect.config import DetectConfiguration
from sigdetect.detector.pypdf2_engine import PyPDF2Detector

configuration = DetectConfiguration(
    PdfRoot=Path("/path/to/pdfs"),
    OutputDirectory=Path("./out"),
    Engine="pypdf2",
    PseudoSignatures=True,
    RecurseXObjects=True,
    Profile="retainer",   # or "hipaa"
)

detector = PyPDF2Detector(configuration)
result = detector.Detect(Path("/path/to/pdfs/example.pdf"))
print(result.to_dict())

Detect(Path) returns a FileResult dataclass; call .to_dict() for the JSON-friendly representation (see Result schema). Each signature entry now exposes bounding_box coordinates (PDF points, origin bottom-left). When PNG cropping is enabled, crop_path points at the generated image. Use Engine="auto" if you want the single-pass defaults that prefer PyMuPDF (for geometry) when available.

---

Library API (embed in another script)

Minimal, plug-and-play API that returns plain dicts (JSON-ready) without side effects unless you opt into cropping:

from pathlib import Path

from sigdetect.api import (
    CropSignatureImages,
    DetectMany,
    DetectPdf,
    ScanDirectory,
    ToCsvRow,
    Version,
    get_detector,
)

print("sigdetect", Version())

# 1) Single file → dict
result = DetectPdf(
    "/path/to/file.pdf",
    profileName="retainer",
    includePseudoSignatures=True,
    recurseXObjects=True,
)
print(
    result["file"],
    result["pages"],
    result["esign_found"],
    result["sig_count"],
    result["sig_pages"],
    result["roles"],
    result["hints"],
)


# 2) Directory walk (generator of dicts)
for res in ScanDirectory(
    "/path/to/pdfs",
    profileName="hipaa",
    includePseudoSignatures=True,
    recurseXObjects=True,
):
    # store in DB, print, etc.
    pass

# 3) Crop PNG snippets for FileResult objects (requires PyMuPDF)
detector = get_detector(pdfRoot="/path/to/pdfs", profileName="hipaa")
file_result = detector.Detect(Path("/path/to/pdfs/example.pdf"))
CropSignatureImages(
    "/path/to/pdfs/example.pdf",
    file_result,
    outputDirectory="./signature_crops",
    dpi=200,
)

Result schema

High-level summary (per file):

{
  "file": "example.pdf",
  "size_kb": 123.4,
  "pages": 3,
  "esign_found": true,
  "scanned_pdf": false,
  "mixed": false,
  "sig_count": 2,
  "sig_pages": "1,3",
  "roles": "patient;representative",
  "hints": "AcroSig:sig_patient;VendorText:DocuSign\\s+Envelope\\s+ID",
  "signatures": [
    {
      "page": 1,
      "field_name": "sig_patient",
      "role": "patient",
      "score": 5,
      "scores": { "field": 3, "page_label": 2 },
      "evidence": ["field:patient", "page_label:patient"],
      "hint": "AcroSig:sig_patient",
      "render_type": "typed",
      "bounding_box": [10.0, 10.0, 150.0, 40.0],
      "crop_path": "signature_crops/example/sig_01_patient.png"
    },
    {
      "page": null,
      "field_name": "vendor_or_acro_detected",
      "role": "representative",
      "score": 6,
      "scores": { "page_label": 4, "general": 2 },
      "evidence": ["page_label:representative(parent/guardian)", "pseudo:true"],
      "hint": "VendorOrAcroOnly",
      "render_type": "typed",
      "bounding_box": null,
      "crop_path": null
    }
  ]
}

Field notes

• esign_found is true if any signature widget, AcroForm /Sig field, or vendor marker is detected.
• scanned_pdf is a heuristic: pages with images only and no extractable text.
• mixed means both esign_found and scanned_pdf are true.
• roles summarizes unique non-unknown roles across signatures.
• In retainer profile, emitter prefers two signatures (client + firm), often on the same page.
• signatures[].bounding_box reports the widget rectangle in PDF points (origin bottom-left).
• signatures[].crop_path is populated when PNG crops are generated (via CLI --crop-signatures or CropSignatureImages).

---

Configuration & rules

Built-in rules live under src/sigdetect/data/:

• vendor_patterns.yml – vendor byte/text patterns (e.g., DocuSign, Acrobat Sign).
• role_rules.yml – signer-role logic:
  • labels – strong page labels (e.g., “Signature of Patient”, including Parent/Guardian cases)
  • general – weaker role hints in surrounding text
  • field_hints – field-name keywords (e.g., sig_patient)
  • doc_hard – strong document-level triggers (relationship to patient, “minor/unable to sign”, first-person consent)
  • weights – scoring weights for the above
• role_rules.retainer.yml – retainer-specific rules (labels for client/firm, general tokens, and field hints).

You can keep one config YAML per dataset, e.g.:

# ./sample_data/config.yml (example)
pdf_root: ./pdfs
out_dir: ./sigdetect_out
engine: pypdf2
pseudo_signatures: true
recurse_xobjects: true
profile: retainer    # or: hipaa
crop_signatures: false   # enable to write PNG crops (requires pymupdf)
# crop_output_dir: ./signature_crops
crop_image_dpi: 200
detect_wet_signatures: false   # opt-in OCR wet detection (PyMuPDF + Tesseract)
wet_ocr_dpi: 200
wet_ocr_languages: eng
wet_precision_threshold: 0.82

YAML files can be customized or load at runtime (see CLI --config, if available, or import and pass patterns into engine).

Key detection behaviors

• Widget-first in mixed docs: if a real /Widget exists, no pseudo “VendorOrAcroOnly” signature is emitted.
• Acro-only dedupe: multiple /Sig fields at the document level collapse to a single pseudo signature.
• Parent/Guardian label: “Signature of Parent/Guardian” maps to the representative role.
• Field-name fallbacks: role hints are pulled from /T, /TU, or /TM (in that order).
  • Retainer heuristics:
  • Looks for client and firm labels/tokens; boosts pages with law-firm markers (LLP/LLC/PA/PC) and “By:” blocks.
  • Applies an anti-front-matter rule to reduce page-1 false positives (e.g., letterheads, firm mastheads).
  • When only vendor/Acro clues exist (no widgets), it will emit two pseudo signatures targeting likely pages.
• Wet detection (opt-in): With detect_wet_signatures: true, the CLI runs an OCR-backed pass (PyMuPDF + pytesseract/Tesseract) after e-sign detection. It emits RenderType="wet" signatures for high-confidence label/stroke pairs in the lower page region. Missing OCR dependencies add a ManualReview:* hint instead of failing.

---

Smoke tests

Drop-in smoke tests live under tests/ and cover:

• Vendor-only (multiple markers)
• Acro-only (single pseudo with multiple /Sig)
• Mixed (real widget + vendor markers → widget role, no pseudo)
• Field-name fallbacks (/TU, /TM)
• Parent/Guardian label → representative
• Encrypted PDFs (graceful handling)

Run a subset:

pytest -q -k smoke
# or specific files:
pytest -q tests/test_mixed_widget_vendor_smoke.py

---

Debugging

If you need to debug or inspect the detection logic, you can run the CLI with --debug:

from pathlib import Path
from sigdetect.config import DetectConfiguration
from sigdetect.detector.pypdf2_engine import PyPDF2Detector

pdf = Path("/path/to/one.pdf")
configuration = DetectConfiguration(
    PdfRoot=pdf.parent,
    OutputDirectory=Path("."),
    Engine="pypdf2",
    Profile="retainer",
    PseudoSignatures=True,
    RecurseXObjects=True,
)
print(PyPDF2Detector(configuration).Detect(pdf).to_dict())

---

Dev workflow

Project layout

src/
  sigdetect/
    detector/
      base.py
      pypdf2_engine.py
    data/
      role_rules.yml
      vendor_patterns.yml
    cli.py
tests/
pyproject.toml
.pre-commit-config.yaml

Formatting & linting (pre-commit)

# one-time
pip install pre-commit
pre-commit install

# run on all files
pre-commit run --all-files

Hooks: black, isort, ruff, plus pytest (optional).
Ensure your virtualenv folders are excluded in .pre-commit-config.yaml (e.g., ^\.venv).

Typical loop

# run tests
pytest -q

# run only smoke tests while iterating
pytest -q -k smoke

---

Troubleshooting

Using the wrong Python

which python
python -V

If you see 3.8 or system Python, recreate the venv with 3.11.

ModuleNotFoundError: typer / click / pytest

pip install typer click pytest

Pre-commit reformats files in .venv

exclude: |
  ^(\.venv|\.venv311|dist|build)/

Vendor markers not detected
Set --recurse-xobjects true and enable pseudo signatures. Many providers embed markers in Form XObjects or compressed streams.

Parent/Guardian not recognized
The rules already include a fallback for “Signature of Parent/Guardian”; if your variant differs, add it to role_rules.yml → labels.representative.

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License

MIT