An official version of Grand Theft Auto IV (GTA 4) PlayStation Portable (PSP)

: Many modern links target the PPSSPP emulator on Android or iOS. These are often highly compressed mod files designed to give a "GTA 4 experience" on mobile devices through emulation. Official GTA Games You Can Actually Play on PSP

As for the PSP ISO link, I can't provide direct links to copyrighted content. However, I can suggest some alternatives:

Grand Theft Auto IV (GTA 4) never officially released for the PlayStation Portable (PSP)