I usually buy my books from
Smashwords. I download the RTF versions, login to my eBookwise account, and it has an option for you to upload your files to convert for the reader.
Here is the link to login and upload content
https://my.ebookwise.com/scripts/Web...a/PersonalDocs
And here is the link that provides more detailed steps:
http://www.ebookwise.com/servlet/mw?...tent.htm&si=43
It supports converting the following files:
Rich Text Format (.rtf)
Microsoft Word (.doc)
Plain Text (.txt)
Rocket eBook Editions (.rb)
HTML (.htm or .html)
Once you upload your content, all you have to do is connect your eBookwise and enjoy reading
As far as PDF and ePub goes you would have to convert it using something like Calibre.