.DD File Extension
File TypeDiskDoubler Archive
What is a DD file?
Compressed file archive created by Macintosh DiskDoubler for Mac OS Classic; uses the LZ78 compression algorithm; compresses files in place on the hard drive, which are expanded on-the-fly when opened; compressed automatically in the background using AutoDoubler.
DiskDoubler was later replaced by Now Compress and Stuffit SpaceSaver. DiskDoubler is not available for Mac OS X.