Evince is a lightweight document viewer which can open PDFs, OpenOffice Presentations (ODP), Scalable Vector Graphics (SVG), Comic Book Archive files (CBR/ CBZ), PostScript (PS), DjVu and Device Independent (DVI) files, and other formats.
The program started as a Linux project, and there are occasional signs of that in the Windows version. Click File > Open, say, and instead of the standard Windows Open dialog, you'll see Evince's own. This isn't a big deal - it's not exactly difficult to figure out what to do - but it does mean you'll have to spend a little more time figuring out the basics than you might expect.
Otherwise, though, Evince proves very straightforward. Open a document and you can customise its view (full screen or dual page, say), zoom in or out, search for text, print it, and more. And a sidebar displays the document index, thumbnails, layers or attachments, if appropriate.
The program still can't really compete with Adobe or the leading competition for PDF handling. There's no browser plugin, for instance. Its annotation abilities are limited to adding basic text notes. Form handling is weak, and rendering speeds aren't spectacular, either.
Evince's wide file format support is a definite plus, though, and if you'd like to access several of its supported document types from a single program then it could prove a useful tool.