If I use the accessibility options for IE, and tell it to ignore font sizes, I end up with a readable help file.
IE is then unusable due to the large (huge) size of the font.
I found this article, which I think may apply to this. Unless I’m wrong, and believe me that happens, this tells you how to add a text size button to the help file. The format is different, but I think this is what you have before it’s compiled??