You're looking for information on Diablo 2: Lord of Destruction character save files.
This is your actual character data file. It stores your level, stats, skills, quests, and inventory. This is the only mandatory file needed to load your character. .d2x : Stores your character's expansion stash data. diablo 2 lod character save files
Creating "mules" to store excess runes, gems, and set items you've collected. You're looking for information on Diablo 2: Lord
The location of your save files depends entirely on your operating system and the version of the game you are playing. Windows 7, 10, and 11 (Modern Windows OS) and 11 (Modern Windows OS)