Wikipedia has an article that lists some of the ePub programs & conversion programs in it:
It is basically a modified xml format, and if you are into coding, you might be able to do it manually using the samples there.
Apple's iWork suite, "Pages" supports the ePub format for obvious reasons - they would like Authors to submit their work for sale via iBooks.
Both Amazon and Apple have 'how-to' worksheets for their respective Kindle / iBook formats. I have examined both formats briefly - but have yet to find the time & stories to submit through those channels.
A third option, which I have used to produce regular books via .pdf is lulu.com - that is, if you are looking to sell or distribute your work. They print books on demand, and offer the option of selling and distributing work via .pdf. They make very good calendars & photo-books too (Christmas is coming you know
) My own 'store' can be found here:
As for converting existing .pdf files into a .epub or text format, the only thing that comes to mind is selecting the entire document, and copy and pasting it into a text editor of your choice - assuming that the text is not a scanned image. You will get the text - but it will require a ton of editing & review, so this trick is not very practical unless you are dealing with a really _LONG_ .pdf file without images and you don't with to retype the darned thing. Maybe they will come up with something in the future - after all, ePub and Kindles have only been around a few years, and .pdf are still widely accepted and used.
Your initial post only indicated you wanted to convert books for your own private use on the Kindle - are you looking to publish your own work?