HELP! Need to reinstall stock firmware on Galaxy S5! (SM-G900W8) topic

I was running CM 11 until it decided not to work, so then genius me, I went in to TWRP recovery and decided to wipe EVERYTHING. I have nothing left besides download and TWRP recovery mode. I am using JOdin on my mac, but that has only ended in failure as I can neither retrieve a pit file or use one that I have downloaded as it continuously comes up as corrupt. Does anyone know how I can get a non corrupt PIT file?