| .D1 | Progress Software Corporation | File di database | Progress Database | ObjectStore | ESW Capital Group |
| .D2 | Progress Software Corporation | File di database | Progress Database | ObjectStore | ESW Capital Group |
| .DAP | SpeedBit | File di database | Download Accelerator Plus Partial Download | Download Accelerator Plus | SpeedBit |
| .DAT | Unknown Developer | File di database | Game Data | Dragon UnPACKer | Open Source |
| .DATA | Appricon | File di database | Analysis Studio Offline Data | Microsoft Excel | Microsoft Corporation |
| .DB | Dwayne Richard Hipp | File di database | Mobile Device Database File | SQLite | Dwayne Richard Hipp |
| .DB-JOURNAL | Sublime HQ Pty Ltd | File di database | SQLite Rollback Journal File | Microsoft Notepad | Microsoft Corporation |
| .DB2 | Samsung Electronics | File di database | Samsung CCTV Video Information File | Samsung SmartViewer | Samsung Electronics |
| .DB3 | Dwayne Richard Hipp | File di database | SQLite Database File | SQLite | Dwayne Richard Hipp |
| .DB4 | dBase, LLC | File di database | dBASE IV Data | dBase | dBase, LLC |
| .DBA | PDC (Prolog Development Center) | File di database | Turbo Prolog Database | Visual Prolog | PDC (Prolog Development Center) |
| .DBC | Microsoft Corporation | File di database | FoxPro Database File | Microsoft Visual FoxPro | Microsoft Corporation |
| .DBF | dBase, LLC | File di database | Database File | Microsoft Excel | Microsoft Corporation |
| .DBO | The Game Creators | File di database | DarkBASIC Object | The Game Creators DarkBASIC Pro | The Game Creators |
| .DBR | Astonsoft | File di database | DeepBurner Disc Project | DeepBurner | Astonsoft |
| .DBT | Abacus Data Systems | File di database | AbacusLaw Data File | AbacusLaw | Abacus Data Systems |
| .DBV | multisoft Datentechnik GmbH | File di database | Database Variable Field | dBase | dBase, LLC |
| .DBW | Ortus Solutions | File di database | DataBoss Database | DataBoss | Ortus Solutions |
| .DBX | Microsoft Corporation | File di database | Outlook Express E-mail Folder | Microsoft Outlook Express | Microsoft Corporation |
| .DCB | LexisNexis | File di database | Concordance Database File | LexisNexis Concordance | LexisNexis |
| .DCT | Microsoft Corporation | File di database | Dictionary File | QuarkXPress | Quark Software Inc. |
| .DCX | ZSoft Corporation | File di database | Zsoft Multi-Page Paintbrush File | Adobe Photoshop | Adobe Systems Incorporated |
| .DDL | Oracle Corporation | File di database | Data Definition Language File | MySQL | Oracle Corporation |
| .DF3 | Omnis Software | File di database | Omnis Studio Database File Format | Omnis Studio | Omnis Software |
| .DF5 | Omnis Software | File di database | Omnis7 And Omnis Studio Database File | Omnis Studio | Omnis Software |
| .DF6 | Omnis Software | File di database | Omnis7 And Omnis Studio Database File | Omnis Studio | Omnis Software |
| .DIA | Spacetornado Software | File di database | Do It Again Task File | Do It Again | Spacetornado Software |
| .DMO | Wouter van Oortmerssen | File di database | Cube 2: Sauerbraten Demo File | Cube 2 Sauerbraten | Open Source |
| .DMU | Interscape | File di database | Musicnizer Database File | Musicnizer | Interscape |
| .DNL | LexisNexis | File di database | Concordance Database File | LexisNexis Concordance | LexisNexis |
| .DQL | Sapphire Group | File di database | DataEase Database | DataEase | 4ThePeople Limited |
| .DQY | Microsoft Corporation | File di database | Excel Query File | Microsoft Excel | Microsoft Corporation |
| .DRI | Microsoft Corporation | File di database | Microsoft SQL Server Replication File | Microsoft SQL Server | Microsoft Corporation |
| .DSK | Power Software Ltd | File di database | General Disk Image | PowerISO | Power Software Ltd |
| .DSN | Cadence Design Systems | File di database | OrCAD Design File | OrCAD PCB Designer | Cadence Design Systems |
| .DXI | ZPAY Payroll Systems, Inc | File di database | PayWindow Database File | PayWindow | ZPAY Payroll Systems, Inc |
| .DXL | IBM | File di database | Domino XML Language File | Microsoft Notepad | Microsoft Corporation |
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