Opening a signed PDF and seeing a yellow warning banner saying the signature is "unverified" or "unknown" is alarming, but it usually doesn't mean the signature is fake. It typically means the viewer can't confirm the identity of the signer โ which is a different problem with a straightforward explanation.
The Difference Between Verified and Valid
PDF digital signatures have two separate properties that are often confused. Validity means the document hasn't been changed since it was signed โ the signature's cryptographic hash matches the document content. Verification means the signer's identity has been confirmed by a trusted certificate authority. A signature can be valid (unaltered) but unverified (identity not confirmed), which is the most common case for everyday electronic signatures.
The "unverified" warning usually means: the signature is cryptographically valid, the document hasn't been tampered with, but the viewer doesn't recognize the certificate used to create the signature as coming from a trusted authority.
Why Most Electronic Signatures Show as Unverified
Simple electronic signatures โ typed names, drawn signatures, or signature images placed on a PDF โ don't use cryptographic certificates at all. They're images placed on the page, not cryptographic operations. Adobe Reader's signature validation only applies to cryptographic digital signatures with certificates. A typed or drawn signature is just an image; the "unverified" warning doesn't apply to these because there's no certificate to verify.
If you're seeing an "unverified" warning, the signature was created as a cryptographic digital signature โ but using a self-signed certificate (one not issued by a recognized certificate authority) or a certificate from an authority not in the viewer's trust list.
Self-Signed Certificates
Anyone can create a digital certificate and sign a PDF with it. A self-signed certificate proves the document hasn't changed since signing, but doesn't prove who the signer is โ because anyone could create a certificate with any name. Browsers and PDF viewers don't trust self-signed certificates by default, hence the unverified warning.
If you trust the sender and just need to confirm the document is intact, the validity status is what matters. Right-click the signature in Adobe Reader โ Signature Properties โ click "Show Certificate" to see the certificate details and determine whether it's the signer you expected.
When Verification Actually Matters
For most business contracts, NDAs, and everyday agreements, the verification status of a digital signature is less important than having a clear record of who signed, when, and what they signed. An email thread showing the signed PDF returned from the signer's known email address is strong evidence of agreement regardless of certificate status.
Verification matters in specific regulated contexts: government document submissions that require certified signatures, financial transactions requiring verified identity, legal filings where the signature must be attributable to a specific identified individual. In these cases, a certificate from a trusted Certificate Authority (CA) like DocuSign, Adobe Sign, or a qualified trust service provider provides the verifiable identity chain that satisfies the requirement.
How to Get a Verified Signature
For signatures that should show as verified in PDF viewers, the signer needs a digital certificate issued by a Certificate Authority that's in Adobe's Approved Trust List (AATL) or the viewer's trusted root store. These certificates are obtained from commercial CAs (DigiCert, GlobalSign, Comodo) or through dedicated e-signature platforms that provide signing certificates to their users as part of the service.
E-signature platforms like DocuSign and Adobe Sign use CA-backed certificates, which is why their Sign PDF signatures typically show as verified. For everyday document signing without these platforms, an unverified-but-valid signature is sufficient for most purposes and the verification warning can be understood in context rather than treated as evidence of a problem.