For a digitally signed document (which might have been signed several times), you can view the differences (if any) between a signed version and the current version you have.

To compare a signed document with the current version, do as the following:

A signed version will be automatically saved each time you sign a PDF with a digital signature. If a digitally signed document was modified, you can still view the signed version without the modification. For a document digitally signed several times, you can view each signed version without the changes made after each signature was applied. All signed versions along with their corresponding digital signatures are listed in the Digital Signatures panel.

To view a signed version of a digitally signed PDF, do as the following:

Many business or other practical applications need digitally-signed documents to be verifiable for months or years after signing. However, the signed document can be no longer verifiable if the signer’s certificate has expired or been revoked, or with some other reasons.

1. Open the PDF containing the signature, do one of the followings:

By default, Foxit PDF Editor will check the certificate revocation status while validating a signature if the certificate used to sign a PDF file chains up to a certificate designated as a trusted anchor. Revocation checks are performed based on the revocation information embedded in the digitally signed PDF document, the digital signature, or the Certificate Revocation List (CRL). To view the certificate revocation information, please do the following: 

By default, Foxit PDF Editor verifies signatures when the document is opened. An icon appears on the left top of Signature Validation Status message box to indicate the signature status. The signature state appears in the Signature Panel.

The signature of a certified or signed document is valid if you and the signer have a trust relationship. The trust level of the certificate indicates the actions for which you trust the signer. 

To set the trust level: 

By default, Foxit PDF Editor will verify signatures when the document is opened, and will check the certificate revocation status while verifying signatures. If you want to change the setting, please go to File > Preferences > Signature, and uncheck the corresponding option in Signing & Verifications group. For more information, please refer to “Signature Preference”. 

To modify a signature after signing the document:

1. Right-click the signature with the Hand command and choose Clear Signature. The signature will be cleared and only a blank signature field will be left.
2. Click the blank signature field with the Hand command, and create a new signature. See also “Creating signature appearance”.

To delete a signed signature:

A PDF is signed to indicate your approval. The signature is flattened, so it cannot be resized and moved after signing the document. Multiple people can sign a PDF more than once. When you sign a document, your digital signature appears in the signature field. The appearance of the signature depends on your preferences.