Convert your book to ePub (a proper eBook format
). You can then use an ePub editor such as Sigil (a free download) to create a TOC, or tweak your book in any way that you wish.
In all honesty, ePub is what you should be using here. It's the industry standard for eBooks, and there are lots of very good ePub viewers for the PC if that's what you use to read on.