The best tool out there is called "Calibre". calibre is a FREE and open source e-book library management application developed by users of e-books for users of e-books. It has a cornucopia of features. Calibre can convert from a huge number of formats to a huge number of formats. It supports all the major e-book formats. The full list of formats can be found on their website. The conversion engine has lots of powerful features. It can rescale all font sizes, ensuring the output e-book is readable no matter what font sizes the input document uses. It can automatically detect/create book structure, like chapters and Table of Contents. It can insert the book metadata into a "Book Jacket" at the start of the book