There are alternatives to pdf's for creating e-books and one free program which is quite handy can be downloaded free and fully functional from
EbooksWriter
This program allows you to produce e-books as .exe files which can therefore be downloaded and read by anyone, even if they don't have Adobe on the machine they download it to. It's pretty intuitive to useand comes with a full manual too.
When promoting a free e-book, don't overlook the torrent sites either - making and uploading torrents is not difficult and can potentially expose your book to a much wider audience. To spread your book this way you'll just need a small piece of free software to create the torrent, a free bitorrent client (the software that allows you to upload/download bt files) then upload it to a site like PirateBay.org for others to download and "seed" - in other words, continue to make the file available for others.
(don't be put off by the name, torrents are only dodgy if they involve trading of copyrighted material).
Good luck with the book!
Mo