Some nice PDF tricks on none other than life hacker ...
Make custom PDF notepaper
Convert files to PDF online
Annotate PDF's with Skim
Password protect PDF's
Merge PDF files
Edit PDF's with PDF Tools
Speed up your PDF reader
Manage your PDF library in iTunes
Convert that whiteboard to PDF
Create a PDF from any document
Learn all of that here
Source: http://lifehacker.com/software/lifehacker-top-10/top-10-pdf-tricks-289583.php
