Issue/Question
How do I sign a PDF using Adobe Reader or Adobe Acrobat?
Resolution
The most up-to-date Adobe Acrobat or Adobe Reader will be needed. It can be downloaded from here. Other programs, including the PDF readers that come with macOS (Preview), Windows (Reader), and any web browser with built-in PDF reader capabilities will not have full functionality of Acrobat or Reader and may not give the ability to sign a PDF.
For a step-by-step guide on signing a PDF or creating a signature, see this Adobe guide.