there are several, but no perfect viewer.
ANDS-pdf is strictly a pdf, but I haven't tried it, and word on the street is that it doesn't like big files.
If you do a little bit of work, you can get PICTODS to convert pdf's to work on Comic Book DS, but the quality goes down. Also, in my experience, if your document is more than 300 pages, it starts slowing way down from that point forward.