If you're not using an iPod, you can ignore the first set of steps in the article, but the rest applies.
PDF is an Adobe format, not a PC format. It can be read by the built-in Preview app. Mac OS X's "Cocoa" user interface shares a common foundation for PDF, so support is quite natural. Adobe Acrobat is also available for Mac, but Preview is much faster.
DOC can be read by TextEdit, which also comes with the computer, as well as by Apple's iWork word processor Pages. XLS can also be read by iWork (Numbers, the spreadsheet app), but the format can't be read without iWork or another office suite like Microsoft Office for Mac.