Select all files for the character or characters you wish to copy over, right click, and choose Copy.Use File Explorer to navigate to C:\Users\(Your PC Username)\Saved Games.You can play your original Diablo II (2000) offline single-player characters on the Diablo II: Resurrected client by manually copying over the character save files from the Diablo II (2000) folder to the Diablo II: Resurrected folder. Diablo II (2000) and Diablo II: Resurrected are independent games.
