With Quartz being built upon PDF technology, it's actually quite easy to convert to and from PDFs in MacOS X. For now, I'll leave the converting to alone, as you want to know how to convert from.
By deafult, the PDF file should open in MacOS X's Preview application. When opened here, you can use the File menu to select Export. From there, you can choose the format you wish, including JPG, TIFF, and a host of others. Just click save after you have selected the format, and Preview will quickly convert your file to the type you wish.