Why are my download going to notepad and are unreadable?

every time i try to download something that needs to be read, it goes to my notepad and its just a bunch of jumbled letters and symbols that are totally unreadable and makes no sense, can someone please tell me who to fix this, I'm uming my daughter tried to set this up but has done something wrong and now she doesnt remember how to go back and fix it, thanks in advance