You can digitally sign a PDF in several different ways, including Adobe Acrobat, Apple's Preview app, and mobile apps, among other options.
Here is a guide that shows you how to sign a PDF document in Microsoft Edge. Signatures are basically used to get or provide consent or approval on documents like contracts, legal documents, ...
Adobe's PDF format has support for document footers. You can use this capability to add a footnote to up to three different areas at the bottom of a PDF document ...