$300 to put a stamp on a PDF file

I use Acrobat on my mac occasionally to put a stamp on PDF file, highlight some text with a highlighter, or combine a few pages together in a document (I also use automator a lot). My Acrobat 8 license came with my ScanSnap scanner.

Usually the documents I need to work with are on my PC, so to save time and hassle I thought I would see how much Acrobat 9 cost, anticipating $50–$100. It is $300!