How to Fix Unknown Digital Signature Validity in Adobe Reader
Question details
The user is attempting to verify a digitally signed PDF but receives an error stating the certificate signature has an unknown validity.
- Product
- Adobe Reader XI
- Device & OS
- not provided
- Scenario
- Verifying a digital signature on a secure PDF document.
- Observed behavior
- Adobe Reader reports the certificate signature as unknown because the signer or the issuing certificate is not recognized in the local trusted identities list.
Ensure that the document was signed by a legitimate party and that you have a secure way to verify the authenticity of the signer's certificate before adding it to your trusted list.
Add the Certificate to the Trusted Identities List
Manually trusting the signer's certificate resolves the unknown validity error, provided you are certain of the document's authenticity.
By default, PDF readers only trust certificates issued by known Certificate Authorities (CAs). If a sender uses a self-signed certificate or a private enterprise certificate, you must manually add it to your trusted identities to validate the signature.
Click or right-click on the digital signature showing the 'Unknown Validity' status in the PDF, and select 'Signature Properties' from the context menu.
In the properties window, click the 'Show Signer's Certificate' button to open the certificate viewer.
Navigate to the 'Trust' tab within the certificate viewer, and click the 'Add to Trusted Certificates' button. Confirm any security prompts that appear.
Check the box to 'Use this certificate as a trusted root' and select the options to trust certified documents. Click 'OK' to save the settings.
Close the certificate viewer and click the 'Validate Signature' button in the Signature Properties window. The status should now update to valid.
Try WPS PDF for Secure and Easy Document Signing
If you frequently encounter frustrating certificate validation errors in heavy PDF readers, consider switching to WPS Office. The built-in WPS PDF tool is lightweight, secure, and offers excellent compatibility for viewing, editing, and managing digitally signed documents.
- 1. Open PDF in WPS Office: Launch WPS Office and open your digitally signed PDF document.
- 2. Navigate to the Protect Tab: Click on the 'Protect' tab located on the top ribbon.
- 3. Verify or Add Signatures: Click on 'Sign Document' to apply your own signature or verify existing signatures within the file seamlessly.
Frequently Asked Questions
Why does a PDF signature show as 'validity unknown'?
This happens when your PDF software does not have the signer's digital certificate stored in its list of trusted identities. Without a pre-established chain of trust, the software cannot confirm if the signature is authentic.
Is it safe to add a certificate to trusted identities?
It is only safe if you personally know the sender or can independently verify the certificate's origin. Never trust a certificate from an unknown or suspicious source, as this could pose a security risk to your system.
How can I automatically update trusted certificates?
Many PDF programs feature a Trust Manager setting. In Adobe Reader, you can navigate to Preferences > Trust Manager and check the box to 'Update Now' under the Adobe Approved Trust List (AATL) section to fetch globally trusted certificates automatically.
Does WPS Office support digital signatures on PDFs?
Yes, WPS Office's PDF tool fully supports viewing, verifying, and applying digital signatures, ensuring your electronic documents remain secure and legally compliant.
