Suggestions for making Help Files?

As one of my collateral duties, I update the user documentation for our software. They didn’t really have any when I started and I foolishly volunteered to go ahead and do it all. I don’t really mind, and now that I have the basic documentation done, updating doesn’t take me more than an hour or so. But right now it’s just one huge Word document. I liked Word because it was pretty quick and easy to make a clickable table of contents. But unless I lock it down and put a lot of restrictions on it, it’s still an editable Word Document. I’d like to move it to maybe html or .hlp format, but I’m not certain of the best way of doing that. A quick google search turns up a ton of programs that will help create both an html help file, and a .hlp windows help file. Does anyone have any experience with a specific program (preferably free) that they recommend? Or perhaps another option or suggestions about creating help files for an application in general?
Thanks!

The industry standard is Robohelp, but it’s pretty seriously not free. Googling for Robohelp alternatives may turn up something interesting.

It’s not free, but in my work as a training development manager, I use RoboHelp to create online help files. It’s very easy to use, and you can also import images (which can be helpful when the written instruction gets too complicated).

Here’s a link to information about the product from Adobe. I’m sure there are other programs out there that do as good of a job and probably for less money, but that’s been the gold standard where I’ve worked.

Edited to add: **Ultrafilter ** beat me to it! But yeah, it’s seriously the gold standard. I’ve been doing this for over a decade and it’s the one to get if you have the budget.