If you can get them cheap, files are a good starting point when you try your first few blades. But if you really want to make a knife, use steel that is known to you. Otherwise the heat treat is a longish trial and error or a guess.
Don't get me wrong, old files are lots of fun and I've made a few small knives with them. But when I really want to make a knife, I don't start with an unknown steel.
On edit: what you want to make is more of a short sword. There are better steel choices for a prybar/knife than a file!