The file is profile.bin, which has nothing to do with your game characters, but with my file you will have access to ALL skins for ALL characters + 65280 gold keys for opening the golden box in Concordia.

It's simple - on a Steam license, put it in "C:Users"User Name"DocumentsMy GamesBorderlands The Pre-SequelWillowGameSaveData"Your SteamID 64""

On a pirated version: search for “profile.bin” in the game folder and replace it; if it’s not in the game folder, look in “My Documents.” I play on a license myself, so I don’t have the opportunity to advise pirates