Pdf Signature Checker

Free online tool. All processing is client-side. No signup needed.

How to Use the Pdf Signature Checker

1. Enter your input values above
2. Results update automatically
3. Copy or download the output

What is a Pdf Signature Checker?

A PDF Signature Checker validates digital signatures embedded in PDF documents — verifying whether the document was truly signed by the claimed signer and hasn't been modified since signing. Digital signatures on PDFs are legally binding in many jurisdictions (eIDAS in EU, ESIGN Act in US), used for contracts, government forms, invoices, and legal documents. This tool checks: signature validity, signing certificate chain (is it from a trusted CA?), document integrity (any changes post-signing?), and timestamp validity.

How Does It Work?

Upload a signed PDF. The checker extracts the digital signature(s) and: (1) verifies the cryptographic hash against the document content (integrity check — detects ANY modification), (2) validates the signer's certificate chain against trusted root CAs, (3) checks certificate expiration and revocation status (OCSP/CRL), (4) validates any timestamp from a Time Stamping Authority (TSA), (5) reports whether the signature is VALID, INVALID, or INDETERMINATE with a detailed explanation. All processing is client-side.

Formula

PDF Signature Structure (PKCS#7/CMS):\n\nSigned PDF = Original Document + Signature Dictionary\n\nSignature includes:\n• Signed hash of document content (SHA-256 typically)\n• Signer's X.509 certificate\n• Optional: Timestamp Token from TSA\n• Optional: CRL/OCSP revocation evidence\n\nValidation:\n1. Hash current document content\n2. Compare with signed hash in signature\n3. If match → document not modified since signing\n4. Validate certificate chain → root CA\n5. Check certificate not expired at signing time\n6. Check certificate not revoked (OCSP/CRL)\n7. If all pass → Signature VALID

Who Uses This Tool?

• Legal professionals verifying signed contracts are authentic and unmodified
• Government agencies validating digitally signed PDF forms and applications
• Businesses verifying vendor and client signed agreements
• Auditors checking document integrity in regulatory submissions
• Anyone receiving a digitally signed PDF who wants to verify it's genuine

Pro Tips

• A VALID signature proves: (1) the document hasn't been modified since signing, (2) the signer's certificate was valid at signing time. It does NOT verify the signer's identity beyond the certificate
• Long-term validation (LTV) includes CRL/OCSP responses and timestamps embedded in the PDF — necessary for documents that need to be verified years later
• A signature can be VALID even if the certificate has since expired — what matters is that the certificate was valid AT THE TIME of signing
• Multiple signatures on a PDF are validated independently — each signer signs the document as it existed at their signing time. Signatures can be added sequentially

Frequently Asked Questions about Pdf Signature Checker

What's the difference between digital and electronic signatures?

Digital signature = cryptographic (PKI-based, mathematically verifiable, tamper-evident). Electronic signature = any electronic indication of agreement (typed name, scanned signature, checkbox 'I agree'). Digital signatures are a secure subset of electronic signatures.

Can I trust a VALID digital signature?

It proves: (1) document not modified since signing, (2) the certificate holder (or someone with their private key) signed. It does NOT prove the signer intended to sign or that the certificate wasn't stolen. That's a legal/judgment question.

Free online Pdf Signature Checker — no signup, 100% client-side processing. All data stays in your browser.