This is a discussion on Opening pdf files if cant vdwnload adobe reader within the iPad Apps forums, part of the iPad App Store category; How....?...
There are a number of PDF viewing/annotating apps for the iPad, including a version of Adobe Reader.
Other apps you might want to look at:
iBooks (will read PDF files only)
GoodReader (read and annotate PDF's, and other on and offline file management stuf)
PDF Expert (read, annotate, the ability to shuffle, add, copy, or delete pages, and other stuff)