Welcome to our community, Bonnie
I think you'll find the same (or dearth of) answers here on the Adobe forums as you found on TECHWR-L.
WinHelp files are really old technology. Microsoft really tried to fool everyone into thinking WinHelp was dead when they released Vista. Of course it still works under Vista and Windows 7 and may require an additional download to make it work depending on whether it's 32 or 64 bit, but work it still does.
However, digitally signing a HLP file is likely something you will find doesn't exist. And it's quite logical if you think about it. As you are still using .HLP format, you are now among a very small minority of users. To create something like a digital signature and make it work would require an investment of time and money. And since this format is dying, I'd be very surprised to see anyone putting any real effort into something with zero payback.
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