The Mobipocket Reader is a FREE tool that can be a great way to read your favorite ebooks on your computer screen, but it also doubles as a quick and easy way to convert some files to a format you can use on your Kindle.
Drag your epub, html, doc, .rtf, .txt, .pdf, excel or powerpoint files right into the right window pane of the main Mobipocket Reader window. You will see the conversion indicator, and when it is finished, you will see your book opened in the reader. Click the words eBooks in the left pane to close the reading view and return to your list of books pane where you originally dragged the book that has just been converted.
Your book will now appear in the list with any others you have opened with your Mobipocket Reader. Right click any book and choose Open containing folder to open the folder where all these converted books are stored. Drag that .prc file right to the Documents folder on your Kindle. When you disconnect (safely) your Kindle from your USB connection and your computer,and turn it on, your newly converted book will appear on the main home screen to treat just like any other Kindle book.
Oh... a .prc file is one of the file types your Kindle can read with no trouble a'tall. Isn't that convenient?
Down and dirty... my kind of file converter!