From the sound of it, it must be an EBook

For info on ebooks and readers check out http://www.mobileread.com/

FREE BOOKS form mobilereader

Other resources for free ebooks in many formats:

http://www.ebooklobby.com/

http://www.mslit.com/default.asp?mjr=FRE

Nice post with many options:

http://www.friedbeef.com/2007/04/09/best-places-to-get-free-books-the-ultimate-guide/