A digital signature can be placed in a document, once you acquire a digital ID inside a certificate file. A digital signature makes it possible to verify that no changes have been made since the document was signed. If changes were made, a comparison can identify the modifications.
Signatures can be placed directly, or incorporated into reusable signature schemes. See Add a signature scheme for detailed steps.
To sign or sign and certify a document from the Security tab select the appropriate tool:
Sign: Place a visible or invisible signature on the page.
Certify: Place a signature on the page (use the drop-down list to select visible or invisible) and add restrictions to document use.
After your first signature is created, the Sign tool places that signature or the one you defined as default on your page at the specified location. Similar placement applies to Certify.
A document can be signed only using the top part of the Sign/Certify panel, or it can be signed and certified using the bottom part of the panel. See Signing and Certifying Documents. All created signature schemes appear in the relevant part of the panel, ready to be selected for use.
When documents are secured by Certificate Security, it acts as your signature, because it verifies to recipients of your PDF files that you are indeed the sender and that the content can be trusted.