The files you may find online labeled as "GTA 4 PSP ISO" are typically of older GTA titles or completely different games modified to look like GTA 4. Why an Official GTA 4 PSP Port Doesn't Exist
Assuming you've made your decision, here's a step-by-step guide to download a GTA 4 PSP ISO file: Gta 4 Psp Iso File -
: PS3 (original) or via backward compatibility on newer systems if supported. The files you may find online labeled as