A digital signature can be placed in a document, once you have acquired 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 to can show what changed.
Signatures can be placed directly, or can be incorporated into reusable signature schemes.
Signature schemes can be created using the New Signature Scheme wizard, accessed by clicking Add in the Sign/Certify panel. If you have no saved schemes, you can create the first one by clicking Sign or Certify at Security > Sign and Certify. After providing a name and description for the scheme, you accept the Digital ID offered or click Add for another one. Then you choose to just sign the document or also certify it - that means that you limit the permitted actions in the PDF file - allow no changes, form filling only or form filling and commenting. Then you define the appearance of your signature - the wizard proposes a standard appearance. Click Finish to have the scheme saved.
To sign or sign and certify a document from the Security ribbon choose 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 choose 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 chosen location. Similarly for Certify.
A document can be just signed 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, this 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.
Note
You can place a handwritten signature in your document from Security > Sign and Certify > Handwritten Signature. In provides no security protection. It is treated as a stamp, but does not appear in the Stamps panel, nor in the Signatures panel. It appears in the Comments panel (all stamps are listed there) so it can be reviewed, commented and more.