Because the PSP hardware is significantly less powerful than the systems required to run Uncharted 4, a functional ISO file for the PPSSPP emulator does not exist. Why you cannot find a legitimate link: Platform Incompatibility

To run Uncharted 4 smoothly on your Android device using PPSSPP, ensure your device meets the following system requirements:

Stay safe, respect game developers, and keep exploring—there are plenty of real adventures waiting for you on Android.

You cannot play Uncharted 4 on Android via PPSSPP. Anyone promising otherwise is trying to scam you. Stick to actual PSP games for the best emulation experience.