Officially, Diablo IV does not have an offline mode. It is an online-only game, even for the single-player campaign. This means a "paper" or official manual does not exist for this process because the feature does not exist in the retail version of the game.
Common Issues and Solutions
If you have a physical copy of Diablo IV for PS4, PS5, or Xbox Series X, follow these steps to skip the initial 90GB download (though you still need a license check): diablo iv offline mode install
While you can install the game files via the Battle.net launcher, Steam, or console stores, you must be logged into an account and connected to the internet to launch the game or access your characters. Why Players Want It vs. Why It's Missing Officially, Diablo IV does not have an offline mode