Seeing a signature panel is not the same as validating a digital signature. A proper review asks four separate questions: is a signature object present, what part of the file was signed, is the cryptographic signature valid under a trusted certificate path, and is that result acceptable for your purpose?
PDFCheck helps with the first two questions. Use a trusted PDF reader or your organization's approved signature-validation service for certificate trust, revocation, timestamp, and policy decisions.
Four Layers of Signature Review
1. Signature presence
The file contains one or more PDF signature dictionaries. This is a structural fact, not proof that the signature is valid.
2. Signed byte coverage
The PDF's ByteRange identifies which bytes were covered. Incremental updates can exist after a signature, so review whether later changes are permitted and expected.
3. Cryptographic and certificate validation
A validator checks the signature value, certificate chain, trust anchors, validity period, revocation information, and any trusted timestamp.
4. Business or legal acceptance
Your policy, jurisdiction, contract, and evidence requirements determine whether the result is sufficient. Technical validity alone does not answer every legal question.
What PDFCheck Shows
The PDF Signature Checker parses signature dictionaries and reports available fields such as signer name, reason, location, signing time, subfilter, certificate strings, permissions, and ByteRange coverage.
If you need help interpreting a reader's warning first, use the invalid PDF signature guide, then return to the full trust and policy checks below.
Boundary: this is structural inspection. PDFCheck does not cryptographically verify the signature contents, decide that a certificate is trusted, query revocation services, or establish the signer's real-world identity.
Step-by-Step Verification
1. Obtain the file through a trusted channel
Confirm the sender and keep the received file unchanged. Re-saving or editing it can alter the signed bytes.
2. Inspect its signature structure
Use PDFCheck for an initial view of signature presence, available identity fields, timestamps, and byte coverage.
3. Open the original in an approved validator
Review the signature status, certificate path, trust source, revocation result, timestamp result, and reported document changes. Adobe documents this process for Acrobat and Reader.
4. Investigate warnings
An unknown signer may mean the certificate is not trusted in your environment. An invalid signature may mean the signed bytes changed. An expired signing certificate may require a valid trusted timestamp and historical validation data.
5. Apply your acceptance rules
For regulated, financial, employment, or legal documents, follow the receiving organization's policy and obtain professional advice where needed.
Common Misunderstandings
- A visible signature image is not a digital signature. It may be only a picture or typed name.
- A signer name field is not verified identity. Trust comes from certificate validation and the identity process behind it.
- “Signed” does not mean “unchanged forever.” PDFs can contain permitted incremental updates; the validator should explain what changed after signing.
- Not every electronic signature has the same legal effect. Under the EU eIDAS framework, a qualified electronic signature has a specific equivalence to a handwritten signature; other electronic signatures are treated differently.
Sources
- Adobe: validate digital signatures
- ETSI Electronic Signatures and Trust Infrastructures
- EU eIDAS Regulation
Bottom line: use PDFCheck to inspect signature structure, then complete cryptographic and trust validation in an approved system.