Sumatra PDF is a slim, free, open-source PDF viewer for Windows.

Why another PDF reader?
Sumatra has a minimalistic design. Simplicity has a higher priority than a lot of features.

It's small and starts up very fast.

It's designed for portable use: it's just one file with no external dependencies so you can easily run it from external USB drive.
[License: Freeware| Requires: Win XP/2003/Vista/Windows7 | Size: 1.20 MB]