By "it's downloaded on notepad" do you mean, whenever you download a quest, it has the .qst extention, but the icon of it is notepad? If so, that just means that it'll try opening them in notepad when you double click it, so the extention must have been associated with notepad somehow, but it should still be readable by Zelda Classic. Have you actually tried loading quest files that are like that, in ZC?