How to Validate Digital Signatures in Adobe Acrobat
Summary :
Learn why a question mark appears on a digital signature in your PDF and discover how to verify digital signatures and remove the question mark in Adobe Reader.
Table of Contents
In a PDF file that has been digitally signed, a question mark on a digital signature in a PDF usually indicates that the signature’s validity is unknown or unverified.
On this page, you’ll find the causes of the issue, and how to validate digital signatures to remove question marks from digital signatures in PDF.
How to Validate Digital Signature in PDF
Adobe Acrobat, a widely used PDF software, offers a way to validate digital signatures in PDF documents.
This feature is crucial for verifying the authenticity and integrity of documents, especially in legal, business, and official communications.
To begin, download and install Adobe Acrobat Reader from Adobe’s official website. This is the free version of Acrobat Pro.
Step 1. Open your PDF document in Adobe Acrobat.
Open a PDF in Adobe Acrobat
Step 2. Right-click (or Ctrl-click on a Mac) on the digital signature and select “Validate Signature.” A pop-up window will appear showing the signature’s validity.
Check the Signature Validation Status
Step 3. In the pop-up window, click “Show Signature Properties.”
Access Signature Properties
Step 4. Click “Show Signer’s Certificate” in the Signature Properties dialog.
Check Signer’s Certificate
Step 5. In the Certificate Viewer, go to the “Trust” tab and click “Add to Trusted Certificates” to allow Acrobat to trust future signatures from this signer.
Add This Digital Signature to Trust Identities
Step 6. Follow the prompts to confirm your trust settings, typically by selecting actions you trust the signer for.
Set Signature Trust Options
Step 7. After adjusting the trust settings, click the digital signature again. Acrobat will re-validate the signature using the updated trust settings, and the status will change to “Signature is valid”.
Update and Revalidate the Digital Signature
Great job, you’ve successfully removed the question mark from the PDF!
Require Certificate Revocation Checking
Adobe Acrobat Reader includes an option that ensures the certificate used for signing is validated for trustworthiness during the digital signature verification process.
Enabling this option is a crucial step in confirming the signer’s identity and ensuring the signature can be trusted.
Step 1. Open the PDF with digital signatures in Adobe Acrobat Reader.
Step 2. Click the menu button in the upper-left corner and select “Preferences” from the dropdown.
Go to Preferences
Step 3. In the “Preferences” menu, go to the “Signatures” tab and click the “More” button in the Verification section.
Click More in Verification
Step 4. Enable the option “Require certificate revocation checking to succeed wherever possible during signature verification.”
Require Revocation Checking
Free Acrobat Reader or Pro?
You might wonder, “Can I validate PDF signatures in the free Adobe Acrobat Reader, or do I need a paid subscription to Adobe Acrobat Pro?”
The answer is yes—you can validate PDF signatures using the free Adobe Acrobat Reader. It includes the necessary features to verify digital signatures on PDF documents.
This functionality ensures the authenticity and integrity of the signature, confirming that the document hasn’t been altered after signing and that the signer’s identity is verified.
While Adobe Acrobat Pro, the paid version, offers advanced features like creating, editing, and signing PDFs, the free Acrobat Reader is more than enough for validating signatures.
Why Can’t I Validate Signatures in PDF?
If you’re unable to validate signatures in a PDF, there could be several reasons. Here are some common issues and possible solutions:
Outdated Software
Ensure you’re using the latest version of your PDF reader (like Adobe Acrobat Reader). Updating your software can often resolve validation issues.
Conversion to Image
If a signed PDF is printed or altered (e.g., printed to PDF using certain methods), the signature may be converted into an image, which can’t be validated as a digital signature.
Correct Opening Method
To validate signatures, open the file in Adobe Acrobat Reader or Acrobat, not in a web browser. Browsers may limit functionality, including signature validation.
Signature Validity Unknown
When the software fails to recognize the certificate used to sign the document, you’ll need to import the signer’s certificate or the certificate authority (CA) that issued it into your trusted store. Refer to the detailed steps above to make the signature valid.
Expired or Revoked Certificate
If the certificate used for signing is expired or revoked, the signature can’t be validated. Contact the signer for an updated certificate or a new signed document.
Modified Document
If the document was modified after it was signed, the signature will be invalid. You’ll need to obtain the original, unmodified document to validate the signature.
Unsupported Signature Algorithm
Your PDF reader may not support the algorithm used to create the signature. Try using a different reader or ask the signer to use a more widely supported algorithm.
Corrupted File
If the PDF is corrupted or damaged, signature validation may fail. Try obtaining a new copy of the file from the source.
Security Settings
Your PDF reader’s security settings might be blocking signature validation. Check the settings to ensure signature validation is enabled.
Missing Required Elements
Some signatures require additional elements, such as timestamps, to be valid. Ensure all necessary components are included in the signature.
Internet Connection Issues
Some readers require an internet connection to check things like certificate revocation lists. Ensure you have a stable internet connection.
Compatibility Issues
The signature may have been created using a method or format that your PDF reader doesn’t support. Try opening the file in a different PDF reader or software.
