They only care about the number of characters. If you're attaching the document, you can go over, and obviously they can't count the characters in Adobe. But if it's obviously too long, I guess 10 pt. would be better to make them think it's shorter than it is. I'd say 12 or 10 pt. is ok, it doesn't really matter either way. I'd also recommend single spacing it if you haven't already done so...it looks more professional and shorter, too.