TDT document format is used by Daylight THOR-Merlin System, software used for storing and retrieving chemical information. TDT files store data in plain text, but but the syntax is rather convoluted.

TDT files store a thesaurus of chemical concepts that are helpful for users who speak different languages or with varied level of chemical expertise. TDT is rather format uncommon as it is used chiefly by scientist and researchers.