Four alternative PDF readers

Adobe's free PDF reader has long been a standard for handling its extremely popular document format, but it's a bloated animal, and the version incorporated in your web browser can take a long time to load. Fortunately, you aren't limited to using it to view PDF files. Here are four alternatives:
Sumatra PDF is an ultra-lightweight and open-source portable application. The emphasis with Sumatra PDF is not on the number of features and the wide-ranging abilities of the application, but instead on speed. It loads almost instantly, renders pages extremely quickly, and thanks to a huge number of keyboard shortcuts, you can zip through nearly any document with ease.
Preview is Apple's free PDF viewer, built into the OS. Preview has quite a few features often only found in commercial PDF software, like the ability to drag and drop pages between documents, page extraction, encryption, and text annotation. In addition to viewing PDF files, Preview can display over two dozen other file formats making it quite a versatile little viewer.
Foxit is a polished Acrobat-alternative that, on top of cleanly displaying PDF files with a minimal interface, also has a host of handy features — all packed into a lightweight 6MB package. For instance, when filling out PDF forms, you can save your progress in the form and return later to finish filling it out. While both the free and the Pro version allow you to annotate text, insert graphics and drawings, and insert links, the free version adds a Foxit stamp on each page you annotate; the pro version removes the marking.
PDF-XChange boasts fast load times and basic functionality that outpaces the basic functionality of Adobe Reader. With PDF-XChange you can open and browse PDF documents, perform simple page annotations with drawings and text, and type outside of preset form boxes by using the PDF-XChange typewriter tool to place text wherever you want. Advanced features like reorganizing pages and text extraction are only available in with the Pro upgrade. PDF-Xchange is available as a portable application.