An H3 file is used to verify a Wii U game .APP file’s integrity. You will encounter an H3 file if you download a Wii U game from Nintendo eShop. An H3 file also exists if you extract a game from a disc. The H3 file will be in the game data folder with APP and other Wii U files if you copy a game to your computer to emulate it.
To open an unknown H3 file, tell Windows which program should open it. Go to Windows Settings then to Apps. Click on apps’ file associations. Select the H3 file type. Choose a program to open H3 files. Check the box “Always use this app for .H3 files”.
The H3 extension can be used by various programs, not just Wii U games. Be careful with H3 files from unknown sources. They may contain malware.
Similar extensions are sometimes mistakenly used instead of .H3: .j3, .b3, .g3, .he, .hr, .hw, .j3, .m3, .n3, .t3. Check the spelling of the extension if solutions to open H3 files fail. The file may be unrecognizable if the extension is misspelled or changed.
Heroes of Might and Magic III