I completely forgot to ask! A week ago our (dumb) heroes were against a 4-armor wizard, and they kept attacking him by normal means (they eventually realized this was not the best strategy).
However it raised a question: if armor is equal to or greater than the damage rolled, there's something like a "minimum 1 damage" rule? I remember something like this, but I can't find anything about it in the pdf. Maybe it was in the red book? Or it's just a refuse from D&D?