| .DCA | IBM | Ficheiros de Texto | DisplayWrite Document | Advanced Computer Innovations WordPort | Interscape |
| .DCF | Sony Mobile Communications | Ficheiros de Texto | DRM Content Format File | DRM Packager | Sony Mobile Communications |
| .DE | Interscape | Ficheiros de Texto | DrawExpress Diagram File | DrawExpress | Interscape |
| .DESC | Electronic Arts | Ficheiros de Texto | Battlefield 2 Map Description File | Battlefield 2 | Electronic Arts |
| .DFM | Open Source | Ficheiros de Texto | Pascal File | Notepad++ | Don Ho |
| .DGS | TES | Ficheiros de Texto | Dagesh Pro Document | TES Dagesh Pro | TES |
| .DH2 | Pursuit Software Ltd. | Ficheiros de Texto | Report Viewer File | Pursuit CRM | Pursuit Software Ltd. |
| .DIZ | Unknown Developer | Ficheiros de Texto | Description In Zip File | Microsoft Notepad | Microsoft Corporation |
| .DL | Microsoft Corporation | Ficheiros de Texto | Zoo Tycoon 2 Data File | Zoo Tycoon 2 | Microsoft Corporation |
| .DNE | Norsys Software Corp | Ficheiros de Texto | Netica Text File | Norsys Netica | Norsys Software Corp |
| .DOC | Microsoft Corporation | Ficheiros de Texto | Microsoft Word Document (before The 2007 Version) | Apache OpenOffice | Apache Software Foundation |
| .DOCM | Microsoft Corporation | Ficheiros de Texto | Word Open XML Macro-Enabled Document | Apache OpenOffice | Apache Software Foundation |
| .DOCS | Unknown Developer | Ficheiros de Texto | Document | Unknown Software | Unknown Developer |
| .DOCX | Microsoft Corporation | Ficheiros de Texto | Microsoft Word Open XML Document | LibreOffice | The Document Foundation |
| .DOCXML | Microsoft Corporation | Ficheiros de Texto | Microsoft Word XML Document | Microsoft Word 2016 | Microsoft Corporation |
| .DOK | Nenad Hrg | Ficheiros de Texto | DesktopOK Icons Layout File | DesktopOK | Nenad Hrg |
| .DOX | Microsoft Corporation | Ficheiros de Texto | Visual Basic Binary UserDocument | Microsoft Visual Studio | Microsoft Corporation |
| .DP | Stefan Hagel | Ficheiros de Texto | Text Document | Microsoft Notepad | Microsoft Corporation |
| .DPO | DECAdry | Ficheiros de Texto | DECAdry Express Business Cards Business Card | DECAdry Express Business Cards | DECAdry |
| .DROPBOX | Dropbox, Inc. | Ficheiros de Texto | Dropbox Shared Folder Tracker | Dropbox | Dropbox, Inc. |
| .DRP | DÖRR EDV-Beratung | Ficheiros de Texto | DReport Document | DReport | DÖRR EDV-Beratung |
| .DSC | Kingsoft | Ficheiros de Texto | Kingsoft Design Science Equation File | Kingsoft Office | Kingsoft |
| .DSO | Microsoft Corporation | Ficheiros de Texto | Microsoft Visual Studio Workspace Data | Microsoft Visual Studio | Microsoft Corporation |
| .DVI | The Evince Team | Ficheiros de Texto | Device Independent Format File | Evince | The Evince Team |
| .DWD | DiamondWare Ltd. | Ficheiros de Texto | DiamondWare Digital Audio File | Wi-Fone | DiamondWare Ltd. |
| .DX | Digital Equipment Corporation | Ficheiros de Texto | DEC WPS Plus File | Microsoft Notepad | Microsoft Corporation |
| .DXB | Autodesk, Inc. | Ficheiros de Texto | Drawing Exchange Binary | Autodesk AutoCAD | Autodesk, Inc. |
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