Signing the PDF on Mac can be a little complex than you can imagine if you are used to word documents or standard text files. Luckily, macOS has several methods through which you can add the signature to PDF, all using the tools instead of requesting you to download any specific apps. As you get the PDF files by mail that you have to sign, the procedure of print file, signing on a dotted line, scanning files, then returning can be a little monotonous. Luckily Apple has included the feature to electronically sign the PDF file via Preview, a feature that is available on all Mac running the OS X Lion or further.