Add a signature button to the navigation pane. Click Tools to open the certificate toolbar. Display "Digital Signature", "Time Stamp", "Verification Signature" and other contents. Click Digital Signature to sign the document. Use the mouse to select the signature location, add a digital signature or signature graphic at the selected location, and lock the document after selecting the signature, so that the signature cannot be added. Instead of locking the document after signing, you can add another signature.