| dcw | Draft Choice for Windows Drawing |
| dcy | NETSCAN Decay Search Results |
| dd | OMA Download Descriptor |
| dd2 | OMA Download Agent v2 Descriptor |
| ddb | Protel 99SE Design Database |
| ddb | TINA Shape Library Database |
| ddd | Verity Server Data |
| ddd | Digital Tachograph Data |
| dde | ABBYY Lingvo Dictionary Error Log |
| ddg | Deltadrive GRS Database |
| ddg | MAP GMS Installation Document |
| ddg | DucatiDiag Data File |
| ddi | MAP IEC Document |
| ddl | Ovation Pro DDL |
| ddoc | DigiDoc Digital Signature |
| ddp | Dinkey Dongle Parameter File |
| ddr | DDRemote Saved Parameters |
| ddr | MAP Parameterisation Document |
| dds | MAP Service Document |
| ddu | MAP dlms User Association Document |
| ddy | ASHRAE Design Conditions Design Day Data |
| dea | Drug Enforcement Administration Data |
| debuglog | MyDefrag Debug Log |
| dee | Creator Circuit Description File |
| def | SmartWare Definition Data |
| defxml | Danea Easyfatt Data |
| dek | Memorize-It Deck File |
| del | Lucene Deleted Documents Data |
| dem | Vflo Digital Elevation Model Data |
| den | XMVB Density Data |
| deos | Driver Easy Offline Scan Data |
| deploy | ClickOnce Deployment Data |
| desg | Stuffit DropSegment Data |
| dess | Microsoft Device Emulator Saved State Data |
| det | Act! Email Message |