PDF files are rapidly spreading across the internet (and that is a good thing). PDFs are a handy way to read documents exactly as they were intended, without having to worry about whether you had the right program or the right fonts.
One of the most popular programs used for viewing PDFs is Adobe Acrobat Reader (now known as simply "Adobe Reader"). Although Adobe Reader is a free program, this little program is also free and does nearly the same thing.
While I have nothing against Adobe Reader, it is very slow to start up. That is not a problem with Foxit Reader. It starts virtually instantly, even with the largest PDF files.
FoxIT Reader only works on Microsoft Windows.