.DUC File Extension
File TypeAction Replay Max DS Save File
What is a DUC file?
Saved game created by the Action Replay Max DS, a hardware device used to apply cheat codes to Nintendo DS and DS Lite handheld console games; saved in Action Replay Max DS's proprietary format, but can be converted to a traditional .SAV file and loaded with a Nintendo DS emulator.
The Shunyweb website can be used to convert DUC files to SAV files. You can also use the program ARDStoSAV.exe.