If your file is in a raw ISO format, right-click the game inside Dolphin, select Properties , go to the Format tab, and convert it to RVZ .
However, the risks cannot be overstated. Downloading and executing unknown files from the internet is dangerous, and the act is unequivocally on the wrong side of the law. The safest and most rewarding path is to find an affordable used copy of Call of Duty: Modern Warfare 3 on eBay or at a local game store, rip the ISO yourself from your legally owned disc, and then use scrubbing and compression techniques to create your own "extra quality" archive. This allows you to enjoy the full game with peace of mind and a clear conscience. If your file is in a raw ISO
Ensuring the compression hasn't downsampled the textures, which would lead to a blurry mess on modern displays. The safest and most rewarding path is to