To alter a PDF on a MacBook, begin with the in-built Preview app. It is already there on your Mac and will allow you to add text, highlight certain passages, place a signature there, and even rearrange and eliminate whole pages. To do more difficult tasks such as editing scanned text or format transformation, you may obtain such applications as Adobe Acrobat or PDF Expert. In the vast majority of everyday change, Preview is free, quick and does the trick.