| dcpil | Delphi Compiler Symbolic Information Data |
| dcr | Delphi Component Resource |
| dct | Delphi Component Template |
| dcu | Delphi Compiled Unit |
| dcuil | Delphi .NET Compiled Unit |
| dcurl | Curl Detached Applet |
| dd | DataFlex Data Dictionary |
| dd32 | x64dbg Data |
| dd64 | x64dbg Data |
| dda | GLBasic ASCII Scene Data |
| ddb | ProWorx NXT Descriptor Data with Blocking |
| ddd | Alpha Five Data Dictionary |
| ddf | Diamond Directive File |
| ddf | IAR System C-SPY Device Description Data |
| ddf | ProWorx NXT Descfriptor Data File |
| ddl | Data Definition Language File |
| ddm | Alpha Five Data Dictionary Memo |
| ddp | Delphi Diagram Portfolio |
| ddr | FileMaker Pro Database Design Report |
| dds | Amazon Lumberyard DirectDraw Surface Data |
| ddw | GLBasic World File |
| ddx | Alpha Five Data Dictionary Index |
| dec | VersaPro Declaration File |
| dectest | Python Decimal Arithmetic Based Test Cases Data |
| def | C++ Definition File |
| definition | Apple Automator Data Type Definition |
| defs | BlueJ Settings File |
| dem | Delphi Edit Mask |
| dem | Turing DEM File |
| deo | Creator Simulator Compiled Module |