The PPSSPP emulator can only run PSP games. No ISO file will magically turn into the Frostbite-engine FIFA 17 you see on PS4/Xbox One.
Open the PPSSPP application. Use the built-in file browser to navigate to the folder where you saved the .iso file. Click on the game icon to launch it. Troubleshooting Common Performance Issues download fifa 17 iso file for ppsspp install