Some mods designed for the official Steam version (currently version 15.20+) may not be backwards compatible with version 15.11.01.
Ensure you have all sequential parts (part01 through the final part) in one directory before extracting part01 using a tool like WinRAR or 7-Zip . Monster.Hunter.World.v15.11.01-CODEX.part04.rar
The file is the fourth segment of a multi-part compressed archive containing the "Master Edition" of Monster Hunter: World - Iceborne , specifically version 15.11.01 , released by the scene group CODEX around June 2021. File & Release Overview Some mods designed for the official Steam version
For the CODEX version, save files are typically stored in: C:\Users\Public\Documents\Steam\CODEX\582010\remote . specifically version 15.11.01