| 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 |
| del | Creator Simulator Compiled Module |
| del | Creator Simulator Temporary Data |
| dem | Creator Simulator Temporary Data |
| dem | Delphi Edit Mask |
| dem | Turing DEM File |
| deo | Creator Simulator Compiled Module |
| dep | IAR System Dependency Data |
| dep | Visual Studio Package and Deployment Wizard Dependency File |
| depend | Code::Blocks Dependencies File |
| deployproj | RAD Studio Deployment Manager Configuration |
| des | Creator Simulator Mozart Source Code |
| developerprofile | Xcode Developer Profile Data |
| dex | Android Compiled Executable |
| df | OpenEdge ABL Data Definition |
| df1 | Omnis Native Data File |
| df2 | Omnis Native Data File |
| df3 | Omnis Native Data File |
| df4 | Omnis Studio Database File |
| df6 | Omnis Studio v6 Database |
| dfac | DreamFactory ActiveX Control |
| dfd | ABC Dyadic Functions Data |
| dfm | Delphi Form |
| dfn | Delphi Definition File |
