How to Automatically Validate Digital Signatures in PDF Forms
Question details
The user wants to configure their PDF software to automatically validate digital signatures on forms returned by colleagues, avoiding manual checks and invalid signature warnings.
- Product
- Device & OS
- not provided
- Scenario
- Receiving and reviewing signed PDF forms from colleagues where the signatures need to be automatically recognized as trusted.
- Observed behavior
- The digital signatures display as 'Signature Not Valid' or 'Signature Validity is Unknown' even after enabling the basic 'Verify Signatures When Document Opens' setting.
Ensure you have requested and received the public keys (certificate files) from the colleagues who signed the document, as automatic validation cannot succeed without a trusted certificate chain.
Configure Automatic Verification and Trust Signer Certificates
Enable automatic signature verification upon opening the document and manually import the signers' public certificates into your PDF reader's trusted identities list.
Simply checking the 'Verify Signatures When the Document Is Opened' option is not enough. The PDF reader must also cryptographically trust the person who signed the document. If the signature relies on a self-signed certificate or a private company certificate, you must add their public key to your local trusted certificates list.
Navigate to Edit > Preferences (or hit Ctrl+K) in your PDF reader. Select 'Signatures' from the left-hand categories. Under 'Verification', click 'More' and check the box for 'Verify signatures when the document is opened'.
Ask your colleagues to export their public certificate (usually a .cer or .p7c file) from their PDF software's security settings and send it to you via email or a secure shared drive.
Go back to Preferences > Signatures. Under 'Identities & Trusted Certificates', click 'More'. Select 'Trusted Certificates' on the left, then click 'Import' to browse and add the certificate files provided by your colleagues.
Select the newly imported certificate from the list, click 'Edit Trust', and check the box to 'Use this certificate as a trusted root' or specifically trust it for 'Certified documents' and 'Dynamic content'.
Manage and Verify PDF Signatures Easily with WPS Office
WPS Office provides a powerful, built-in PDF toolset that allows you to easily view, sign, and manage document security settings, including seamless validation of digital signatures.
- 1. Open the Signed PDF: Launch WPS Office and open the signed PDF form you received from your colleagues.
- 2. Check Signature Status: Click on the digital signature field within the document. WPS PDF will automatically read the signature and display a panel showing whether the signature is valid, invalid, or unknown.
- 3. View Certificate Details: If the validity is unknown, click on 'Signature Properties' to view the signer's certificate. From here, you can choose to trust the certificate for future documents.
- 4. Save Trust Settings: Once the certificate is trusted, close and reopen the document. WPS Office will now automatically validate the signature every time the file is opened.
Frequently Asked Questions
Why does my PDF say 'Signature Validity is Unknown'?
This warning occurs when the document is signed with a certificate that your PDF reader does not currently recognize or trust. The signature hasn't necessarily been tampered with; the software just lacks the public key needed to verify the signer's identity.
Is checking 'Verify Signature When Document Opens' enough to fix the error?
No. While this setting automates the checking process when you open the file, it still relies on your local list of trusted certificates. If the signer's public key isn't in your trusted list, the automated check will still return an 'Unknown' status.
How do I get a colleague's public key?
Your colleague must manually export their public certificate directly from their PDF software's security or signature preferences. They can save this as a .cer or .p7b file and share it with you.
Can I trust all signatures from my company automatically?
Yes, if your company issues signatures using an internal Certificate Authority (CA), you can add the single root CA certificate to your trusted list. All individual employee signatures issued under that root will then be validated automatically.
