While Adobe may have invented the PDF format, it's no secret that Adobe Reader is a bloated program that runs slowly on most computers. We're big fans of Foxit as a lightweight alternative that opens PDF files in a flash. But the How-To Geek just turned us on to Sumatra PDF viewer, an even smaller free and open source PDF viewer.

Sumatra is a single 802KB executable file for Windows. No installation required. That means you can run Sumatra off of a flash drive. You can also set it as your default PDF viewer.

The program opens most of your common PDF files faster than you can say Adobe. It also uses keyboard shortcuts for quick navigation. And it's still under development. The most recent update came out about two weeks ago with a few new features like "save as," and the ability to display recently opened files.