If you've had enough of Adobe's PDF Reader software, I know I have, then get a free alternative called FoxIt Reader.  It does the same thing that the free Adobe Reader does, only it unloads itself from memory when you are done, has a smaller footprint, is faster (for me), and doesn't constantly ask you to register or upgrade or buy anything.  I recommend it to everyone who needs simple PDF support, which is nearly everyone.

What are you waiting for?  Here the link!