Users wanting to verify an electronic signature on a document should take the following steps:
Set your preferences in Adobe Acrobat XI Pro to automatically validate electronic signatures by selecting the 'Preferences' tab/pane (under Edit), then selecting the 'Signatures' category and clicking on the 'More' button adjacent to the 'Verification' option. On the popup window labeled 'Signature Verification Preferences' enable the checkbox labeled 'Verify signatures when the document is opened'.
Open the executed document only in Adobe Acrobat and not another "PDF" viewer program.
Verify the signature (or signatures) in the document as follows by viewing the 'signatures panel' in Adobe Acrobat. Clicking on the 'signature' logo (on the left) should expand details under 'Rev 1: Signed by '. Neither the 'Signature validity' nor the 'Signer's identity' should be listed as 'unknown'. Also, you should see: 'Document has not been modified since this signature was applied.