So you want to publish your book. I did to. My problem was that I didn't just have a word document with writing, I had images. Lots of images.
There are 3 great free software that I want to share with you
1) GIMP 2 - the most fantastic piece of software for digital files
2) Hamster epub converter - will convert your pdf into an epub
3) Calibre and brilliant epub converter.
Both Hamster and Calibre will convert your word document into epubs. If you have images though I encountered major problems getting the images to work with text. I did a children's book and in the end I had to save all my images in GIMP2 in the correct size. It's not enough to resize in word, you have to have the images in the correct size. Even if you save to pdf, both converters use the info from the original images NOT what you see on the word document.