Does Adobe show the message 'Signature validity is UNKNOWN'? There is no need to worry: this does not mean that your signature is invalid. It only means that Adobe cannot currently verify for itself that the certificate had not been revoked at the time of signing.
The document has not been modified since it was signed, and the certificate was valid at the time of signing and issued by a trusted provider. Adobe shows this in the same window.
The message only appears for signatures without LTV information. Signatures placed with Digidentity eSign since June 2026 include this information automatically and will not show this message.
What exactly do you see in Adobe?
In Adobe Acrobat or Reader, open the Signature panel and choose Signature Properties. You will see several lines. This is what they mean:
- The Document has not been modified since this signature was applied
The content is exactly as you signed it. This is good news. - The path from the signer's certificate to an issuer's certificate was successfully built
The certificate comes from a trusted provider on the EU Trusted List. This is good news. - The signer's identity was valid when it was issued
The certificate was in order. No cause for concern. - Revocation checking was not performed
Adobe cannot currently check whether the certificate was ever revoked. No cause for concern, see below. - Signing time is from the clock on the signer's computer
The signature does not contain an official timestamp. No cause for concern, see below.
Only the last two lines cause the 'UNKNOWN' status. This is about missing evidence, not an error in the signature.
⚠ When should you take action?
Only if Adobe shows something other than 'UNKNOWN':
- Red cross or 'Signature is INVALID': the document may have been altered after signing.
- 'The document has been modified': changes other than those permitted were made after signing.
- 'The certificate has been revoked': the certificate was revoked at the time of signing.
- 'The signer's identity is unknown' or 'not trusted': Adobe does not recognise the issuer. This can often be fixed by updating the trust list in Adobe via Preferences > Trust Manager > European Union Trusted Lists (EUTL) > Update Now.
Do you only see 'UNKNOWN', together with the line saying the document has not been modified? Then everything is fine.
Is my signature still valid?
Yes. Whether an electronic signature is valid depends on the situation at the time of signing, not on the day you open the document. This is also how it is laid down in the European eIDAS Regulation.
A signature that was valid when you signed does not become invalid because the certificate expires later. The same applies to a paper contract: it remains valid even if the passport you used at the time has since expired.
Under eIDAS, a qualified electronic signature has the same legal effect as a handwritten signature. That legal effect does not disappear because Adobe shows 'UNKNOWN'.
Why does the message only appear after some time?
The status changes because the certificate used for signing expires, not because anything happens to the document.
- When you sign, your certificate is included in the signature. A certificate is valid for a limited period.
- As long as the certificate is valid, Adobe checks online each time whether it has been revoked. This works, so the signature shows as 'valid'.
- After the certificate's expiry date, the issuer no longer provides revocation status for that certificate. This is standard across the industry, not just at Digidentity.
- Adobe can then no longer check this online. If that information is not stored in the document itself, Adobe shows 'UNKNOWN'.
What is LTV (Long Term Validation)?
LTV is recorded proof, together with an official timestamp, that the certificate was valid at the time of signing. With this information in the document, Adobe can keep verifying the signature even after the certificate has expired.
Signatures placed with Digidentity eSign since June 2026 include LTV automatically. You do not need to do anything.
How do I add LTV information myself?
Was a document signed without LTV, for example earlier or via another platform? You can add LTV information in Adobe Acrobat, as long as the certificate is still valid:
- Open the signed document in Adobe Acrobat while you are online.
- In the Signature panel, right-click the signature.
- Choose Validate Signature and wait until the status is 'valid'.
- Right-click again and choose Add Verification Information.
- Save the document.
An older document already shows 'UNKNOWN'. What now?