If you want to change the font size of the text in the Flash help files then simply go to Internet Explorer and select: View -> Text Size -> large/medium/small etc. When you restart Flash the font size will be changed to match the IE settings.

Why, might you ask is that the way it works? To quote one of my favorite science fiction characters, “I don’t know. I didn’t build the fucking thing.” (Reese, Terminator)