PDF Signoff

PDF Signoff is a local, agent-friendly command-line utility for placing one signature PNG on one or more PDF pages. It can either open a minimal browser UI for human review or apply a previously saved placement profile unattended. An optional L1 stage adds an invisible PDF digital signature for tamper evidence.

The CLI is the product API. Every successful signing invocation writes a separate PDF and emits exactly one reusable placement-profile JSON object on stdout. Status, warnings, and errors are written to stderr.

PDF Signoff is pre-alpha software. Review its output before relying on it.

For compatible AI agents, the portable pdf-signoff skill describes a conservative invocation and output-validation workflow. Install the complete skills/pdf-signoff directory in the agent's skill location; the skill treats the installed pdf-signoff --help as the current command reference.

Installation

PDF Signoff requires Python 3.13 or newer.

python3.13 -m pip install pdf-signoff
pdf-signoff --help

The wheel includes the production Vue/PDF.js review UI. Node.js is not required to run either review or automatic signing from an installed package.

To install the checked-out project with its locked development dependencies:

uv sync --frozen --group dev
uv run pdf-signoff --help

Review Mode

Review is the default mode. This starts a protected one-shot web server on a loopback address, opens the review page in the default browser, and waits until Save is selected:

pdf-signoff report.pdf --signature signature.png > report-placement.json

The UI starts empty when --coords is omitted. Select Place signature, then move over a PDF page to preview the signature and click to add it. The preview is fully clamped within the page. A placement can be moved, resized with its aspect ratio locked, removed from its right-click menu, or removed with the Delete key while selected. A resized width becomes the size for later placements in that review session. The only normal visible toolbar controls are Place signature and Save. Save writes the configured output directly; it does not open a filename dialog or download a file through the browser.

Supply an existing profile to preload editable suggestions:

pdf-signoff report.pdf \
  --signature signature.png \
  --coords report-placement.json \
  --review \
  > reviewed-placement.json

The emitted profile contains the final edited placements, not merely the preloaded suggestions. Closing the browser without saving does not cancel the operation; the CLI continues waiting. Press Ctrl+C to stop it without emitting a profile or creating an output.

Automatic Mode

Automatic signing is always explicit and requires a non-empty placement profile:

pdf-signoff report.pdf \
  --signature signature.png \
  --coords reviewed-placement.json \
  --auto \
  > final-placement.json

Supplying --coords alone never enables unattended signing. --review and --auto are mutually exclusive.

Before using a profile, PDF Signoff requires its page count, listed displayed CropBox dimensions (within 1 PDF point), rotations, and optional required-text conditions to match the current PDF. The source SHA-256 in created_from is informational so a profile can be reused for changing instances of the same form.

Output And Capture

Unless --output is supplied, the output suffix is inserted before the final extension:

report.pdf       -> report_signed.pdf
report.v2.pdf    -> report.v2_signed.pdf

An explicit destination takes precedence over the configured suffix:

pdf-signoff report.pdf \
  --signature signature.png \
  --coords reviewed-placement.json \
  --auto \
  --output /tmp/report-approved.pdf \
  > /tmp/report-approved-placement.json

The input PDF is never modified in place, and input and output may not resolve to the same file. Existing destinations are refused unless --overwrite is explicit:

pdf-signoff report.pdf \
  --signature signature.png \
  --coords reviewed-placement.json \
  --auto \
  --output report-approved.pdf \
  --overwrite \
  > report-approved-placement.json

Output is built in a temporary file in the destination directory and published only after every requested stage succeeds. With --overwrite, replacement is atomic. Without it, PDF Signoff also prevents a destination created by another process while signing from being replaced. Published PDFs use POSIX mode 0644 (owner read/write; group and other read), regardless of the process umask.

On success, stdout is one compact JSON document followed by a newline and the exit status is zero. At the default INFO log level, stderr reports the output path; higher log levels may suppress that informational message. On failure, stdout is empty, the exit status is non-zero, and no partial output is committed. Automation should select an explicit --output rather than parse stderr. Keep stdout separate when an agent needs to capture the final profile while still allowing diagnostics to reach the terminal:

pdf-signoff report.pdf --signature signature.png > placement.json

Placement Profiles

Version 1 profiles use normalized coordinates against the displayed page CropBox after rotation. The origin is at the top left, x increases right, y increases down, values are in the range 0 through 1, and page numbers are 1-based.

{
  "version": 1,
  "created_from": {
    "sha256": "<informational SHA-256 of the source PDF>"
  },
  "match": {
    "page_count": 1,
    "pages": [
      {
        "page": 1,
        "width_pt": 600.0,
        "height_pt": 800.0,
        "rotation": 0
      }
    ],
    "required_text": [
      {
        "page": 1,
        "text": "Employee signature:"
      }
    ]
  },
  "placements": [
    {
      "page": 1,
      "x": 0.62,
      "y": 0.72,
      "width": 0.24,
      "height": 0.045
    }
  ]
}

created_from and match.required_text are optional. PDF Signoff preserves input required-text conditions in the final profile but cannot infer them for a new profile. match.pages must contain exactly one metadata entry for every page from 1 through match.page_count. Each placement must have positive width and height and remain fully within its referenced page. Its physical PDF rectangle must also match the PNG aspect ratio within the backend tolerance; malformed hand-edited profiles are rejected rather than distorted.

Configuration

PDF Signoff uses Onacol with schema-backed YAML configuration. Generate a schema-free template without supplying signing arguments:

pdf-signoff --get-config-template config.yaml

The generated values are:

general:
  log_level: INFO

output_suffix: _signed
default_level: l0
default_signature_width: 0.16
open_browser: true
host: 127.0.0.1
port: 0
l1:
  pkcs12_path: ''
  password_env: PDF_SIGN_PKCS12_PASSWORD
  reason: Internal document approval

Configuration precedence from lowest to highest is:

1. Bundled defaults.
2. One user YAML file: explicit --config PATH, otherwise $XDG_CONFIG_HOME/pdf-signoff/config.yaml, otherwise ~/.config/pdf-signoff/config.yaml.
3. Environment variables such as PDF_SIGNOFF__DEFAULT_LEVEL and PDF_SIGNOFF__L1__PKCS12_PATH.
4. Nested Onacol CLI options such as --output-suffix _approved or --general--log-level DEBUG.

For example:

PDF_SIGNOFF__DEFAULT_LEVEL=l0 \
  pdf-signoff report.pdf \
  --signature signature.png \
  --coords reviewed-placement.json \
  --auto \
  --output-suffix _approved \
  > approved-placement.json

An explicit config file replaces, rather than layers on top of, a discovered user file. Environment variables and ~ in l1.pkcs12_path are expanded after configuration is merged and validated. Port 0 asks the operating system for an available ephemeral port. The review host must parse as a loopback IP address; remote binding is rejected. general.log_level controls application and review-server diagnostics on stderr; DEBUG adds workflow details without logging session credentials or L1 key material.

L0 And L1

--level l0 embeds the supplied PNG at every final placement. Transparency is preserved. L0 does not add a cryptographic signature and makes no claim that the PDF has not subsequently changed. It does not create Adobe Fill & Sign proprietary metadata.

--level l1 first produces the same complete visual result, then adds an invisible pyHanko approval signature over that revision before the output is committed. L1 can detect changes to the covered revision, including changes to the visible image or its placement. It does not prove who controlled the key, who reviewed the document, or whether a certificate should be trusted.

L1 requires a PKCS#12 .p12 or .pfx signer bundle. Configure its path, the name of the password environment variable, and the non-secret reason:

[!TIP] Create a local signer bundle For development or internal use, create a self-signed certificate and bundle it with its private key using OpenSSL. Run this in a private temporary directory; OpenSSL prompts for the bundle password.

openssl req -x509 -newkey rsa:3072 -nodes -days 365 \
  -keyout signer-key.pem -out signer-cert.pem -subj '/CN=PDF Signoff'
openssl pkcs12 -export -out signing.p12 \
  -inkey signer-key.pem -in signer-cert.pem -name 'PDF Signoff'
rm signer-key.pem signer-cert.pem

Move signing.p12 to protected storage. A self-signed certificate is not trusted by default.

l1:
  pkcs12_path: ~/.config/pdf-signoff/signing.p12
  password_env: PDF_SIGN_PKCS12_PASSWORD
  reason: Internal document approval

Then set the password without putting it in command arguments and request L1:

export PDF_SIGN_PKCS12_PASSWORD='read-secret-from-your-secret-store'
pdf-signoff report.pdf \
  --signature signature.png \
  --coords reviewed-placement.json \
  --auto \
  --level l1 \
  > integrity-placement.json

If the configured password variable is absent, an interactive TTY may use a secure password prompt. Non-interactive runs fail instead. Protect the PKCS#12 file and password as private signing credentials. PDF Signoff does not print passwords, private-key material, or sensitive signer details. Missing, invalid, or unreadable credentials fail without committing an output or emitting a profile.

A self-signed certificate can provide integrity and key continuity while still being untrusted. PDF Signoff does not perform public-CA identity validation, certificate trust management, timestamping, revocation embedding, or long-term validation. L1 is not a legal, qualified, or externally verified human signature claim.

Previously Signed Inputs

PDF Signoff refuses an input containing an existing filled PDF cryptographic signature field before opening review or creating output. Rewriting or stamping such a PDF may invalidate its previous signatures.

--allow-signed-input is an expert override:

pdf-signoff previously-signed.pdf \
  --signature signature.png \
  --coords reviewed-placement.json \
  --auto \
  --allow-signed-input \
  > final-placement.json

The override emits a strong warning only to stderr. It permits processing but does not validate previous signatures or claim that any previous signature remains valid.

Local Review Security

Review mode is a local desktop session, not a network service:

• The server accepts only loopback IP addresses and defaults to 127.0.0.1 on an operating-system-selected port.
• One random 256-bit credential protects one signing session. The bootstrap URL transfers it to an HttpOnly, SameSite=Strict cookie and redirects to remove it from the address; bearer authentication is also supported by the backend.
• API requests without the active credential and unrelated browser origins are rejected. No permissive CORS policy is enabled.
• The server exposes only the invocation-selected PDF and PNG, path-free session metadata, fixed frontend assets, and a placement-only save operation. It has no generic file API or directory listing.
• Access logging is disabled to avoid routinely logging token-bearing URLs, and the session is invalidated after its one successful save or server shutdown.

The server uses plain HTTP on loopback, so its session cookie is intentionally not marked Secure. The security boundary assumes the CLI, browser, operating system account, and local machine are trusted. Other processes running as the same user, browser extensions, endpoint compromise, or disclosure of the bootstrap URL are outside that boundary. Do not expose or proxy the review server, share the tokenized URL, or configure it as a multi-user service.

Supported And Rejected Inputs

The MVP supports readable, unencrypted, non-empty normal PDFs and one decodable PNG signature asset per invocation. It supports multiple placements and pages, displayed CropBoxes, non-zero page-box origins, arbitrary normal page sizes, and rotations of 0, 90, 180, and 270 degrees.

It rejects these inputs or invocations conservatively:

• Encrypted or password-protected PDFs.
• Malformed, repaired, unreadable, non-PDF, or zero-page documents.
• Non-PNG or undecodable signature assets.
• Invalid, empty-in-auto-mode, out-of-range, or aspect-inconsistent placements.
• Unsupported profile versions and profile/document page, geometry, rotation, or required-text mismatches.
• An output equal to the input, or an existing output without --overwrite.
• --auto without --coords.
• L1 without available valid signer credentials.
• Previously signed PDFs without --allow-signed-input.

Required-text matching uses text extractable by PyMuPDF. There is no OCR or PDF password-unlock workflow.

Responsibility Boundary

PDF Signoff deliberately does not decide whether a document should be signed. The calling user, agent, or workflow is responsible for deciding:

• Which PDF should be signed.
• Which signature PNG and signing credential may be used.
• Which stored placement profile applies to the document.
• Whether human review is required or unattended --auto is appropriate.
• Whether L0 or L1 meets the workflow's policy and legal requirements.
• Whether the final PDF and emitted profile should be accepted or distributed.

PDF Signoff only validates the supplied inputs and profile, obtains or reviews placements, creates a separate output, optionally seals that revision for integrity, and returns the final normalized profile. An external workflow must provide authorization, identity, approvals, storage, retention, and audit policy.

MVP Non-Goals

The MVP does not provide:

• Legal or qualified electronic signatures.
• Public-CA identity validation.
• Timestamp authorities.
• Long-term PAdES validation, including PAdES LT/LTA.
• OCSP/CRL embedding, certificate-chain trust management, or other revocation and trust services.
• Adobe Fill & Sign proprietary metadata compatibility.
• Handwriting capture or image editing.
• OCR-based automatic signature-position discovery.
• Automatic document or template classification.
• Multi-user server deployment or a remote web service.
• Cloud storage integration.
• PDF form filling beyond signature placement.
• Password-protected PDF support.
• Multiple different signature PNG identities in one invocation.
• An audit database or workflow engine.

Development Verification

The release checks use the Python and Node lockfiles:

uv sync --frozen --group dev
uv lock --check
uv run pytest --cov=pdf_signoff tests/
uv run ruff check .
uv run ruff format --check .
uv run mypy pdf_signoff
uv run tox

cd frontend
npm ci
npm audit
npm run typecheck
npm test
npm run build
npm run test:e2e

The configured Python coverage threshold is 100%. Playwright requires its Chromium browser and host dependencies in the development environment. Building the release artifacts uses uv build; running the resulting wheel does not require Node.js, npm, Vite, Vitest, or Playwright.

License

PDF Signoff is distributed under the MIT license.