If you're tired of waiting for Adobe Reader to launch, waiting again while it loads your document, or reading about its latest security holes, then the STDU Viewer makes an interesting alternative. In our tests it popped up and displayed documents anything up to four times faster, while making less demand on your RAM and other system resources. A tabbed interface lets you open multiple documents at the same time, and when you reopen the program it can quickly restore whatever you were reading in the last session.
Perhaps the best feature of the STDU Viewer, though, is its support for other formats beyond PDF. The most useful is the ability to open XPS documents, but it can also read Comic Book Archives (CBR or CBZ), DjVu and TXT files, even TIFF images.
It's not all good news. The STDU Viewer can't handle more advanced PDF features like encryption or PDF forms, so you'll need to keep an alternative reader around to handle the more difficult files. Still, the speed, tabbed interface, and ability to quickly open even basic PDF and XPS files in the same viewer means the program earns a thumbs up from us.