NWN2 - 1.04 Final Patch Released @ Official Forums

I've downloaded the patch, but it's like my PC doesn't recognize what program or file it is, so when I double-click on it, it wants me to specify what program to open it with.

… what am I doing wrong? How do I patch this game without the auto-patcher?

Just use the UPDATE function when you launch the game; that's always the best way to do it, unless you have a corrupted file, or are using a No-CD patch!!