Is it solid metal, or just a metal sheet covering the wood door frame? If it’s solid metal…well…you need a good drill (AC powered, not battery) and a metal bit. If it’s just a piece of metal over wood, then let me ask you this:
And are you trying to directly drive the screws into it, or trying to drill a pilot hole first, and then drill them in? If you have the right type of screw, you usualy don’t need to drill a pilot hole. And if you are wasting yourtime trying to amke a pilot hole with an underpowered drill and/or wrong bit, then yeah, it’s not going to work.
Speaking of screws, are they sheet metal screws? Are they designed to screw into metal or wood? Most sheet metal screws have a round head with a flat bottom, as oppossed to many wood screws that have a flat head with an angeled bottom. It will also have a coarser thread than a wood screw, usually.
Here’s a sheet metal screw
It might also have a hex head, so that it can be driven with a nut driver in addition to a screwdriver.