If you are looking to play Days Gone on your Android phone using the PPSSPP emulator,
The PPSSPP emulator is designed to run games. Since Days Gone was never released on the PSP, there is no legitimate .ISO or .CSO file for it. If a website claims to have a "Days Gone PPSSPP ROM," it is either: Days Gone Download For Android PPSSPP - isoroms.com PPSSPP