Converting eBooks from PDF to ePub format allows you to read eBooks more easily on your iPad, iPhone, iPod Touch, Sony Reader or other eBook Readers. Some e-readers only support specific formats with their default reader apps.
If you want to install Calibre to convert nearly any (non-DRMed) ebook format into ePub on Windows, Mac OS X, or Linux, go here for more detailed info and screen shots.
* use a pdf to epub website, that you can easily find with Google (just make sure to read the reviews — you don’t want to download and end up with malware!).