If you plan to annotate on a Mac and don't want to downloaded more program like Adobe Reader, you cannot use the built-in Show app that came standard use all Macs. To use the program simply open your pdf. View of annotation options the navigation to Tools > Annotate and name this optional you would see the make.
You cannot and show the marking toolbar at the top by select View > Show Markup Toolbar.
Mark, underline, draw and add notations to the document. Once you are done, make sure to remember.
Changes to the document should can visible inside other programs like Adobe Reader.