You cannot open the .004 file by itself. To access the content inside, you must follow these steps:

Right-click on the first file (the one ending in .001 ).

When large datasets, software, or media collections are archived using , they are often split into smaller chunks.

High-resolution texture packs or "Total Conversion" (TC) mods for games.

The .7z indicates it is a 7-Zip archive, and the .004 indicates it is the fourth part .