| .DAVMOUNT | Microsoft Corporation | Ficheiros de Sistema | Windows Based Script Host | Microsoft Windows | Microsoft Corporation |
| .DBL | Microsoft Corporation | Ficheiros de Sistema | Microsoft Windows XP Product Activation Data | Windows XP | Microsoft Corporation |
| .DDT | Sports Interactive | Ficheiros de Sistema | Football Manager Keep Player Data File | Football Manager 2016 | Sports Interactive |
| .DDZ | AT&T Labs | Ficheiros de Sistema | Adaptec SCO Unix Driver Image | Unix | AT&T Labs |
| .DESKLINK | Microsoft Corporation | Ficheiros de Sistema | Desktop Shortcut | Microsoft Windows | Microsoft Corporation |
| .DESKTHEMEPACK | Microsoft Corporation | Ficheiros de Sistema | Microsoft Windows Theme Pack | Microsoft Windows 8 | Microsoft Corporation |
| .DEV | Bloodshed Software | Ficheiros de Sistema | Dev-C++ Project File | Dev-C++ | Bloodshed Software |
| .DEVICEMANIFEST-MS | Microsoft Corporation | Ficheiros de Sistema | Microsoft Windows Device Metadata | Microsoft Windows | Microsoft Corporation |
| .DEVICEMETADATA-MS | Microsoft Corporation | Ficheiros de Sistema | Device Metadata Package | Microsoft Windows | Microsoft Corporation |
| .DFU | Apple | Ficheiros de Sistema | iOS DFU File | Apple iOS | Apple |
| .DIAGCAB | Microsoft Corporation | Ficheiros de Sistema | Troubleshooting Pack Cabinet File | Microsoft Windows | Microsoft Corporation |
| .DIAGCFG | Microsoft Corporation | Ficheiros de Sistema | Troubleshooting Pack Configuration File | Microsoft Support Diagnostic Tool | Microsoft Corporation |
| .DIAGPKG | Microsoft Corporation | Ficheiros de Sistema | Troubleshooting Pack File | Microsoft Support Diagnostic Tool | Microsoft Corporation |
| .DIT | Microsoft Corporation | Ficheiros de Sistema | Active Directory Information Tree File | Microsoft Active Directory | Microsoft Corporation |
| .DL4 | Lindab | Ficheiros de Sistema | Lindab Dimsilencer File | DIMsilencer | Lindab |
| .DLL | Microsoft Corporation | Ficheiros de Sistema | Dynamic Link Library | Microsoft Visual FoxPro | Microsoft Corporation |
| .DLX | DIAL | Ficheiros de Sistema | DIALux Document | DIAL DIALux | DIAL |
| .DMD | Oracle Corporation | Ficheiros de Sistema | SQL Developer Data Modeler File | SQL Developer Data Model | Oracle Corporation |
| .DMP | Microsoft Corporation | Ficheiros de Sistema | Windows Memory Dump File | Microsoft Visual Studio | Microsoft Corporation |
| .DOH | Geoworks Ensemble | Ficheiros de Sistema | Geoworks Dependency Information File | GEOS (Graphic Environment Operating System) | Geoworks Ensemble |
| .DPB | Susteen, Inc. | Ficheiros de Sistema | DataPilot Backup File | DataPilot | Susteen, Inc. |
| .DRV | Microsoft Corporation | Ficheiros de Sistema | Device Driver | Microsoft Windows | Microsoft Corporation |
| .DS | DAZ 3D | Ficheiros de Sistema | DAZ Studio 1/2 Script | DAZ Studio | DAZ 3D |
| .DSK | Power Software Ltd | Ficheiros de Sistema | General Disk Image | PowerISO | Power Software Ltd |
| .DSR | Activision | Ficheiros de Sistema | Modern Warfare 3 Dedicated Server Recipe File | Call of Duty 4: Modern Warfare | Activision |
| .DSS | The International Voice Association (IVA) | Ficheiros de Sistema | Digital Speech Standard File | DSS Player Lite | Olympus Corporation |
| .DTHUMB | Google | Ficheiros de Sistema | Android Data Thumbnail | Google Android | Google |
| .DUMP | Microsoft Corporation | Ficheiros de Sistema | Dump File | macOS | Apple |
| .DVC | IBM | Ficheiros de Sistema | Lotus 1-2-3 Data | Lotus 1-2-3 | IBM |
| .DVD | Unknown Developer | Ficheiros de Sistema | DOS Device Driver | MS-DOS | Microsoft Corporation |
| .DYC | Xerox | Ficheiros de Sistema | Xerox Printer Driver Configuration File | Xerox CentreWare | Xerox |
| .DYL | Psion PLC | Ficheiros de Sistema | EPOC16:Dynamic Link Library File | EPOC (operating system) | Psion PLC |
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