Searching for usually stems from one of three scenarios:
This is ideal for testing changes without repacking. Doom 3 Pk4 Files Download
Move your downloaded .pk4 files into the base subfolder. This is where the engine looks for game data by default. Searching for usually stems from one of three
The PK4 files come standard with every legitimate copy of Doom 3. Doom 3 Pk4 Files Download
Are you looking to message, or are you trying to get a particular mod running on modern hardware?