The DeepValidator returns an invalid result, even though I can visually see the signature in the document. What is the reason?
Automatically translated
The signature check shows an invalid result even though a signature is visible in the PDF if there is no (or no longer any valid) technical, verifiable signature behind that visible signature graphic.
Most common causes
Only a graphic, no real signature
Some tools only insert an image (“signature image”) without creating a cryptographic signature according to the PDF/ETSI standard. In this case, a validator may see a signature graphic but cannot find a verifiable signature container — the result is “no/invalid signature.”
Document modified after signing
If a PDF is changed after signing (content, pages, objects), the checksum (hash value) no longer matches the original signature, and any trusted validator must report the result as invalid — even if the signature graphic is still displayed unchanged.
Expired or revoked certificate
If the signer’s certificate has expired or has been revoked, the visual signature may still be present in the document, but the cryptographic validation will return “invalid” or “not trusted.”
Faulty or incomplete signature creation
Some signature solutions do not embed the signature correctly on a technical level (incomplete certificate chain, incorrect signature attributes, etc.). The PDF still shows a signature field, but validation fails due to technical inconsistencies.
Signature does not meet ZertES or eIDAS requirements
- Not eIDAS-compliant (EU) typically means:
Only a simple electronic signature is present (for example, a scanned image or click-signature), without the strong identification, sole control over the signing key, and integrity protection required for an advanced or qualified signature. Or no suitable certificate from a recognized trust service provider was used, or the certificate/certificate profile does not meet the requirements for an AdES/QES under eIDAS.
- Not ZertES-compliant (Switzerland) means analogously:
The signature does not meet the requirements for an advanced/qualified electronic signature under Swiss federal law (for example, no recognized Swiss certification authority, no qualified certificate, no approved signature creation device, impermissible profile, etc.).
Practical consequence:
The document may still be electronically “signed” and have some evidential value, but it is not recognized as a qualified or advanced signature within the meaning of eIDAS/ZertES and therefore does not benefit from the special legal status provided there, such as equivalence to a handwritten signature in the case of a QES.
How to proceed
- Check in a PDF reader under the signature details whether a digital signature with a certificate is actually embedded behind it or whether it is only an image.
- Check whether the document was changed after signing (for example, a notice in DeepValidator or in the PDF reader such as “document was changed after signing”).
- Review the certificate details (validity period, revocation status, issuer).
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