Adobe Reader has some great features - such as inserting a signature or filling in forms. However, when sharing out completed forms or PDFs with annotations, the notes do not appear. It seems as though this is best used if annotating and then printing.
New iPad app from Adobe seems to combine the best of a lot of different apps - internal image search like Haiku Deck, record audio on pictures like Speaking Photo, plus even more.
Wondershare lets you edit PDFs from a Mac. It is less expensive than the full version of Acrobat. A great classroom example came from an EdTechTeacher summer workshop participant. She created a Wordle, which she saved as a PDF. Then she inserted a QR code into it that linked back to additional information on her blog.