STDU Viewer is a simple free viewer for a host of file formats: PDF, TIFF, DjVu, XPS, CBR/ CBZ, JBIG2, WWF, FB2, TXT, TCR, PalmDoc(PDB), MOBI, AZW, EPub, DCX and image (BMP, PCX, JPEG, GIF, PNG, WMF, EMF, PSD) files.
Getting started is as easy as clicking File > Open and choosing whatever document you need. Alternatively, drag and drop a group of files onto STDU Viewer and it loads them all, displaying a separate tab for each one (much easier to navigate than the multiple windows of Adobe Viewer). The program can save the current session, too (the documents you have open), and quickly restore this whenever you like.
STDU Viewer has all the core viewing features you'd expect. There are plenty of navigation and zoom options; you can rotate pages, select and copy text or images; there are tweaks for brightness, contrast and gamma, as well as the option to invert colours; and the list goes on.
There's also an unusually capable search tool, with support for both wildcards and regular expressions.
You get a tool to save your document as text files or images, with a customisable file name template helping get the results you need (just use %PN% as a placeholder for the file page number, like "MyDocument_%PN%.GIF".
And, most conveniently, this all comes in a compact and portable application which requires less than 9MB disk space.
There are better PDF viewers around, but if you'll use the wider file format support then this is well worth a look