How to: Add an On-line User Manual to Site?

I’d like to post our 110-page User Manual on our site so that registered users can access it online. We already have a download capability, but the goal is to improve on that. Ideally, the online version would allow for linking the Table of Contents and the Index for quick and easy access. The document has scores of illustrations, was composed in Word and is available in Word 2007 or better or PDF but we can convert its format as necessary to accomplish the goal.

Suggestions or pointers are welcome!