PDF Signature Checker — Free & Private

A free edge API by formatho.com, privacy-first developer tools.

Free, no signup, runs entirely in your browser — your data never leaves your device.

🔓 Free🔒 Zero tracking🚫 No data collection⚡ Edge-fast

Usage

curl --data-binary @signed.pdf -H 'Content-Type: application/pdf' https://pdf-signature-checker-formatho.filesformatho.workers.dev/api
# or: curl -H 'Content-Type: application/json' -d '{"pdf_base64": "..."}' https://pdf-signature-checker-formatho.filesformatho.workers.dev/api

POST a PDF (raw body up to 20 MB, or JSON {"pdf_base64": "…"}). Returns every signature's /ByteRange, signed-byte coverage %, the /Contents placeholder size, SubFilter (adbe.pkcs7.detached, ETSI.CAdES.detached, …), signing time, reason and signer name — plus byte counts of any content outside the signed ranges (unsigned modifications, appended incremental updates) and a structural verdict.

What's checked: whether the signed ranges cover the whole file, whether bytes were appended after signing, how many revisions (%%EOF markers) exist, and AcroForm /SigFlags. This is a structural check — cryptographic verification of the certificate and digest happens client-side in the full tool.

Full parameter reference: /api endpoint.

Privacy-first: the PDF is parsed in-memory at the edge and never logged or stored. For fully offline checking use the browser tool — files never leave your machine.

Full browser tool

Verify PDF signatures entirely client-side, including cryptographic checks: PDF Signature Checker on formatho.com.

All Formatho edge APIs

Browse every free Formatho Worker tool on the Formatho Tools index.