DT filename extension is associated with Apple computers. DT files were used in older Apple operating systems and are now considered obsolete. DT files are not to be manually opened and edited.

DT format is support on Unix-like systems. DT files contained so called forks, that is additional data associated with given document file. The format can support single or multiple forks per file. DT forks can be of arbitrary size and may be even larger the the source file.