There is no official, licensed version of Far Cry 4 for the PSP. Therefore, a legitimate ISO or CSO file (the standard file formats for PPSSPP games) for Far Cry 4 does not exist. Any website claiming to offer a "Far Cry 4 PPSSPP ISO" is misleading you.
The quest for a is a digital ghost hunt. It does not exist, and it never will. But that doesn’t mean you cannot enjoy the spirit of Far Cry on your PSP emulator. The legitimate Far Cry Instincts offers jungle combat, explosive arrows, and vehicle chases that hold up remarkably well on a modern smartphone screen with upscaled resolution.
So when you see websites offering a download for a "Far Cry 4 PPSSPP file," you are encountering one of three things:
Search instead for: