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Right click on the ISO, select open with, then choose default program. Browse to your Dolphin installation, and select the exe file.

Not sure why you're using Adobe reader for a GCN game. I'm going to assume you have the Dolphin emulator. You can try to re-download your game.

Here are a couple of videos showing both Gamecube...

Open WinRAR. Go to options/settings/integration

Look for "Associate WinRAR with" then untick ISO.