| dct | Adobe Illustrator Dictionary |
| dct | Concordance Dictionary Database |
| dct | E-Sword v8 Dictionary Data |
| dct5 | Microsoft Word 5 for Mac Dictionary Data |
| dctmp | DC++ Partially Downloaded |
| dctx | E-Sword v9 Dictionary Data |
| dctxc | Microsoft IME Dictionary Compiler File |
| dcv | DriveCrypt Volume |
| dcw | Draft Choice for Windows Drawing |
| dcy | NETSCAN Decay Search Results |
| dd | OMA Download Descriptor |
| dd2 | OMA Download Agent v2 Descriptor |
| ddat | DivX Temporary Video Data |
| ddb | TINA Shape Library Database |
| ddb | Protel 99SE Design Database |
| ddd | Verity Server Data |
| ddd | Digital Tachograph Data |
| dde | ABBYY Lingvo Dictionary Error Log |
| ddg | DucatiDiag Data File |
| ddg | Deltadrive GRS Database |
| ddg | MAP GMS Installation Document |
| ddi | MAP IEC Document |
| ddl | Ovation Pro DDL |
| ddoc | DigiDoc Digital Signature |
| ddp | Dinkey Dongle Parameter File |
| ddr | MAP Parameterisation Document |
| ddr | DDRemote Saved Parameters |
| ddrt | LeCroy DDR Trace Data |
| dds | MAP Service Document |
| ddt | Oracle Documaker GenData Dataprocessing Rules Data |