Since the "GTA 4 PSP ISO" does not exist, here is what you should download for a high-quality open-world experience on your PSP or emulator (like PPSSPP):
If you are determined to try a "GTA 4 Mod" for PSP despite the warnings: Gta 4 Psp Iso Rom High Quality Download
Disclaimer: This article is for educational and informational purposes only. "Grand Theft Auto IV" is a trademark of Rockstar Games. The PSP (PlayStation Portable) is a trademark of Sony Interactive Entertainment. There is no official version of GTA IV for the PSP. Downloading copyrighted ROMs or ISOs of games you do not own is illegal in most jurisdictions. This guide explains the technical reality and points to legal alternatives. Since the "GTA 4 PSP ISO" does not
Download the actual official ISOs (from your own legally backed-up discs): Download the actual official ISOs (from your own
Where to get high-quality versions: You can buy these games on the PlayStation Store (playable on PS Vita or PSTV) or rip your own UMD discs using a custom firmware PSP. These are the only "high quality" ISOs that exist for the platform.
Many "ROM" sites will force you to disable your ad-blocker, then bombard you with fake "Download Now" buttons. Clicking one installs browser extensions that redirect all your searches to shady ad networks.
Even if you find a file labeled GTA_4_PSP_HD.iso, downloading 1.8GB on a slow connection only to find out it is just Liberty City Stories with a poorly photoshopped cover is a massive disappointment.