Validate Digital Signatures

Validating digital signature allows you to verify, if the document is authentic and no changes were made into it by anyone else other than the author who signed it.

To validate a digital signature:

1. Open the PDF document in Master PDF Editor.
2. Select the signature in the document. You can do this using any of these ways:
   • Click Edit Document on the toolbar, then double-click the signature.
   • Click Hand Tool on the toolbar, then click the signature once.
   • Right-click the signature and select Signature options.

This will bring up the Signature Properties window.

There you can see who signed the document and the signing reason as well as the validation summary: whether the signature is valid or invalid, or if validity is unknown.

Signature is VALID

The signing certificate is trusted, and its parent certificates are trusted. The document content was not altered after signing. If the digital signature is valid, you should see the following message in the Signature Properties window:

Signature is INVALID

Issues occurred when validating the signature. Document was changed or damaged after signing.
Signature validity is UNKNOWN

The signing certificate is not trusted or the parent certificate of the issuing authority (the organization that issued the signing certificate) is not trusted. However, the document was not altered after signing. The following message is displayed in the Signature Properties window:

Making a certificate trusted

For Windows and macOS: You must add the certificate’s open key to the system certificate storage.
For Linux: Click the Information button, view the certificate properties and then press Add to Trusted Identities.

Viewing the signed version of the PDF document

The structure of the PDF format leaves a thin possibility that the original signed content of the document could be replaced by the altered content. And this altered content is then shown when the PDF document is opened. However, the signed version of the PDF document is still available in the file.

To view the version of the document that was actually signed, do the following:

1. Open the PDF document.
2. Switch to the Signatures tab on the left panel.
3. Click Click to view this version.

This displays the original version of the document that was signed by its author and hence prevents forging of the PDF document content.

IMPORTANT: Always view the signed version as described here when opening documents signed with a signature of unknown validity.

More like this:

Document Comparison
Managing bookmarks
Headers and Footers for PDFs