One thing I do recall from .hlp files, is that the text is compressed. Long ago, in a land far away... there was an article in DDJ about it.

Got it... the date is Sept/Oct 1993, 9 years ago, the article itself, by Pete Davis, is in two parts in the series "Undocumented Corner". It's the first two results you get when you do a full text search for "Windows HLP file format". Available for purchose only. Sorry. And sorry, too, I can't give you a more direct link, some people really don't seem to grasp the basics of a hyperlinked medium. And those are the people who are supposed to know better.

You can always try your luck at Wotsit.