Check a PDF's digital signature

What signature validation actually checks

A PDF digital signature answers two different questions, and it's easy to conflate them. The first is integrity: has the signed content changed since it was signed? That's a cryptographic hash comparison — deterministic, and something localdobe can check fully on your device. The second is identity trust: is the certificate that produced the signature actually issued to who it claims, by an authority you trust? That check depends on validating a certificate chain against a trust store — the list of certificate authorities your operating system or browser trusts.

Browsers don't expose that OS-level trust store to web pages, so a signature that's fully intact can still show as "not fully verified" here — that's a statement about what could be checked in-browser, not a defect in the signature. If you need full chain-of-trust verification for legal purposes, use desktop software (like Adobe Acrobat) that has access to your system's certificate store. localdobe is the right tool for checking whether a signed document has been tampered with.

Why local checking matters for signed documents

Documents worth signing — contracts, notarized filings, signed invoices — are exactly the documents you don't want sitting on a third-party server. Most "free" online signature checkers upload your PDF to validate it, which means a contract's full contents (and its cryptographic signature) pass through someone else's infrastructure before you get an answer. localdobe validates and strips signatures using a WebAssembly PDF engine running entirely inside your browser tab: your document is never transmitted, logged, or stored anywhere.

Want the details? Read how PDF digital signatures actually work and what actually happens to your files on online PDF tools.