.H3 File Extension
What is an H3 file?
An H3 file contains an SHA-1 cryptographic hash used to verify the integrity of a Nintendo Wii U game data .APP file. It is referenced by a Wii U game console or emulator (Cemu) and is not meant to be manually opened by a user.
You will most likely only encounter an H3 file if you purchase and download a Wii U game from the Nintendo eShop. You may also encounter an H3 file if you dump a game from a disc using a disc extraction tool.