The 
Signatures tab shows certifications and digital signatures placed on a document (including invisible signatures from services such as DocuSign or digital IDs with embedded timestamps) as well as tools for signing and certifying documents. Users are prompted to open it whenever a PDF that has been certified or digitally signed is opened.
To show the Signatures tab, go to View > 
Tabs > Signatures or press ALT+4.
Certification and Signature Status of a Document
If the current document has been certified or digitally signed, it will be shown on the Signatures tab. The validation status of each digital signature is shown.
To view the details of a signature, click the toggle arrow to its left.
Signatures Tab Toolbar
The Signatures tab toolbar contains several tools for adding and managing digital signatures and certifications.
Sign Document: Creates a signature field and automatically attempts to sign it.
Add Signature Field: Creates a signature field without trying to sign it.
Certify Document: Certifies a document for authenticity.
Validate Signatures: Attempts to validate all signatures in the document.
Preferences: Opens the Signature Preferences.
Working with Digital Signatures