Foxit Reader

Foxit Reader is a free PDF document viewer and printer, with incredible small size, breezing-fast launch speed and amazingly rich feature set. In the past, you have to download a huge PDF Reader from another software company, go through a lengthy installation process and wait for an annoying splash window to disappear just to open a PDF document. Moreover, if you want to annotate a PDF document, you have to pay US$299 to buy that certain PDF software.

Thanks to Karamjit Lal for the update.