| .D2J | Unknown Developer | Developer Files | D2jsp Script File | Unknown Software | Unknown Developer |
| .D4 | Open Source | Developer Files | Dataphor Source File | Dataphor | Open Source |
| .DART | Google | Developer Files | Dart Source Code File | DART | DARTECH |
| .DBA | PDC (Prolog Development Center) | Developer Files | Turbo Prolog Database | Visual Prolog | PDC (Prolog Development Center) |
| .DBML | Microsoft Corporation | Developer Files | Visual Studio OR Design File | Microsoft Visual Studio | Microsoft Corporation |
| .DBP | Microsoft Corporation | Developer Files | Microsoft Visual Studio Visual C++ Database Project | Microsoft Notepad | Microsoft Corporation |
| .DBPRO | The Game Creators | Developer Files | DarkBASIC Professional Project File | The Game Creators DarkBASIC Pro | The Game Creators |
| .DCF | Sony Mobile Communications | Developer Files | DRM Content Format File | DRM Packager | Sony Mobile Communications |
| .DCP | Embarcadero Technologies | Developer Files | Delphi Compiled Package | Delphi (IDE) | Embarcadero Technologies |
| .DCU | Embarcadero Technologies | Developer Files | Delphi Compiled Unit | Delphi (IDE) | Embarcadero Technologies |
| .DCUIL | Embarcadero Technologies | Developer Files | Delphi .NET Compiled Unit File | Delphi (IDE) | Embarcadero Technologies |
| .DCURL | SCSK Corporation | Developer Files | Curl - Detached Applet File | Curl | SCSK Corporation |
| .DD | Sage | Developer Files | Sage MAS 90 Data File | Sage MAS 90 | Sage |
| .DDD | Alpha Software | Developer Files | Alpha Five Data Dictionary File | Alpha Anywhere - Alpha Software | Alpha Software |
| .DDM | Alpha Software | Developer Files | Alpha Five Data Dictionary Memo File | Alpha Anywhere - Alpha Software | Alpha Software |
| .DDP | Embarcadero Technologies | Developer Files | Delphi Diagram Portfolio File | Delphi (IDE) | Embarcadero Technologies |
| .DDX | Alpha Software | Developer Files | Alpha Five Data Dictionary Index File | Alpha Anywhere - Alpha Software | Alpha Software |
| .DEC | Various Developers | Developer Files | Declaration File | Microsoft Notepad | Microsoft Corporation |
| .DEF | Microsoft Corporation | Developer Files | Module Definition File | Microsoft Visual Studio | Microsoft Corporation |
| .DEP | Microsoft Corporation | Developer Files | Windows Dependency File | Microsoft Windows | Microsoft Corporation |
| .DEPLOY | Just Great Software | Developer Files | DeployMaster Installation Project File | DeployMaster | Just Great Software |
| .DEV | Bloodshed Software | Developer Files | Dev-C++ Project File | Dev-C++ | Bloodshed Software |
| .DF1 | Omnis Software | Developer Files | Omnis Native Datafile | Omnis Studio | Omnis Software |
| .DFAC | Unknown Developer | Developer Files | DreamFactory ActiveX Control | DreamFactory | Open Source |
| .DFB | Interscape | Developer Files | Data Flask Formula | Interscape Data Flask | Interscape |
| .DFD | Open Source | Developer Files | ABC Dyadic Functions Data | ABC Programming langauge | Open Source |
| .DFM | Open Source | Developer Files | Pascal File | Notepad++ | Don Ho |
| .DFWEBAPPLICATION | TogetherSoft | Developer Files | Together ControlCenter Development Tool | Together | TogetherSoft |
| .DG | Data Access Worldwide | Developer Files | DataFlex Source Code For A Dialog Box | DataFlex | Data Access Worldwide |
| .DGD | Unknown Developer | Developer Files | DGD Program | Dworkin's Game Driver | Open Source |
| .DGML | Microsoft Corporation | Developer Files | Visual Studio Directed Graph Document | Microsoft Visual Studio | Microsoft Corporation |
| .DGSL | Microsoft Corporation | Developer Files | Microsoft Visual Studio Visual Shader Graph File | Microsoft Visual Studio | Microsoft Corporation |
| .DIAGSESSION | Microsoft Corporation | Developer Files | Diagnostics Session File | Internet Explorer | Microsoft Corporation |
| .DIFF | Matt Mackall | Developer Files | Patch File | Mercurial | Matt Mackall |
| .DIN | 4ThePeople Limited | Developer Files | DataEase Installation Script | DataEase | 4ThePeople Limited |
| .DLG | Crytek | Developer Files | Crysis Dialogue Data File | Crysis | Crytek |
| .DMB | BYOND | Developer Files | BYOND Game Executable | BYOND | BYOND |
| .DMD | Oracle Corporation | Developer Files | SQL Developer Data Modeler File | SQL Developer Data Model | Oracle Corporation |
| .DML | Sybase, Inc | Developer Files | DynaScript File | Internet Explorer | Microsoft Corporation |
| .DMT | DeLorme | Developer Files | XMap Transfer File | XMap | Garmin |
| .DOB | Sublime HQ Pty Ltd | Developer Files | Visual Basic UserDocument | Notepad++ | Don Ho |
| .DOR | Graphisoft | Developer Files | ArchiCAD Geometric Description Language File | ARCHICAD | Graphisoft |
| .DOX | Microsoft Corporation | Developer Files | Visual Basic Binary UserDocument | Microsoft Visual Studio | Microsoft Corporation |
| .DPJ | Delft Spline Systems | Developer Files | DeskProto Project | DeskProto | Delft Spline Systems |
| .DPK | Embarcadero Technologies | Developer Files | Delphi Package | Delphi (IDE) | Embarcadero Technologies |
| .DPL | Embarcadero Technologies | Developer Files | Delphi Package Library | Delphi (IDE) | Embarcadero Technologies |
| .DPR | Niklaus Wirth | Developer Files | Pascal Source Code | MacroMates TextMate | MacroMates |
| .DRC | Open Source | Developer Files | Open Mobile Alliance DRM Rights Object | Microsoft Notepad | Microsoft Corporation |
| .DRES | Embarcadero Technologies | Developer Files | Delphi Compiled Resource File | Delphi (IDE) | Embarcadero Technologies |
| .DS | DAZ 3D | Developer Files | DAZ Studio 1/2 Script | DAZ Studio | DAZ 3D |
| .DSB | Dell Technologies | Developer Files | Dell DataSafe Backup File | DataSafe Local Backup | Dell Technologies |
| .DSK | Power Software Ltd | Developer Files | General Disk Image | PowerISO | Power Software Ltd |
| .DSP | Open Source | Developer Files | Dynamic Studio Professional Module | ModPlug Player | Open Source |
| .DSR | Activision | Developer Files | Modern Warfare 3 Dedicated Server Recipe File | Call of Duty 4: Modern Warfare | Activision |
| .DSU | Schneider Electric | Developer Files | ProWORX Nxt Data Setup | ProWORX | Schneider Electric |
| .DTD | Syncro Soft | Developer Files | Document Type Definition File | Microsoft Notepad | Microsoft Corporation |
| .DTS | CyberLink | Developer Files | DTS Encoded Audio File | CyberLink PowerDVD | CyberLink |
| .DVB | Autodesk, Inc. | Developer Files | AutoCAD VBA Project File | AutoCAD VBA module | Autodesk, Inc. |
| .DWS | Autodesk, Inc. | Developer Files | AutoCAD Drawing Standards File | Autodesk AutoCAD | Autodesk, Inc. |
| .DYLIB | Apple | Developer Files | Mach-O Dynamic Library | Apple Xcode | Apple |
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