It's always – always – important to read those agreements. Another bit in (most, commonly) is that you can't offer your book for less elsewhere. That is, you can't offer it for $10 at Amazon and $7 at B&N and $5 at your website.

There are software tools that can convert to ePub or Kindle formats, mind you. Calibre can do it, for example. Again, though, I've had the best luck with Calibre when converting ePub to Kindle (or vice versa) when the documents are done to standard. Trying to take a DOC or DOCX or RTF and turning it into a quality ePub is a totally different story.