| .CA2 | Embarcadero Technologies | Utviklerfiler | Delphi Install Disk12 File | Delphi (IDE) | Embarcadero Technologies |
| .CA5 | Embarcadero Technologies | Utviklerfiler | Delphi Install Disk11 File | Delphi (IDE) | Embarcadero Technologies |
| .CAP | Microsoft Corporation | Utviklerfiler | Network Monitor Packet Capture Data File | Microsoft Network Monitor | Microsoft Corporation |
| .CAR | Unknown Developer | Utviklerfiler | Car Explorer Data File | Car Explorer | Unknown Developer |
| .CAS | Autodesk, Inc. | Utviklerfiler | Autodesk Cascade License File | AutoCAD Architecture | Autodesk, Inc. |
| .CBA | WinAbility Software | Utviklerfiler | Comic Book ACE Archive | GonVisor | G.A.A. |
| .CBL | IBM | Utviklerfiler | COBOL Source Code File | GNU Compiler Collection (GCC) | GNU Project |
| .CBP | The Code::Blocks team | Utviklerfiler | Code::Blocks Project File | Code::Blocks | The Code::Blocks team |
| .CC | Don Ho | Utviklerfiler | C/C++ Source Code File | MacroMates TextMate | MacroMates |
| .CCC | Open Source | Utviklerfiler | Dev-C++ Code Completion Cache | Dev-C++ | Bloodshed Software |
| .CCN | Clickteam | Utviklerfiler | Compressed Multimedia Fusion File | Multimedia Fusion | Interscape |
| .CCP | Ambiera | Utviklerfiler | CopperCube JavaScript File | CopperCube | Ambiera |
| .CCS | YesSoftware | Utviklerfiler | CodeCharge Studio Project File | CodeCharge Studio | YesSoftware |
| .CD | Microsoft Corporation | Utviklerfiler | Visual Studio Class Diagram | Microsoft Visual Studio | Microsoft Corporation |
| .CDF | Wolfram Research | Utviklerfiler | Computable Document Format File | Wolfram Research CDF Player | Wolfram Research |
| .CDX | Microsoft Corporation | Utviklerfiler | Compound Index File | Microsoft Visual FoxPro | Microsoft Corporation |
| .CDXML | PerkinElmer | Utviklerfiler | ChemDraw XML File | Open Babel | Open Babel development team |
| .CFC | Adobe Systems Incorporated | Utviklerfiler | ColdFusion Component File | Adobe Dreamweaver | Adobe Systems Incorporated |
| .CFG | Unknown Developer | Utviklerfiler | Configuration File | Microsoft Notepad | Microsoft Corporation |
| .CGI | Unknown Developer | Utviklerfiler | Common Gateway Interface Script | Microsoft Notepad | Microsoft Corporation |
| .CGL | Embarcadero Technologies | Utviklerfiler | CodeGuard Error Log File | RAD Studio | Embarcadero Technologies |
| .CH | CA Technologies | Utviklerfiler | Clipper Include File | Clipper | CA Technologies |
| .CHB | Microsoft Corporation | Utviklerfiler | OLE-DB Checkbook File | Unknown Software | Unknown Developer |
| .CI | Microsoft Corporation | Utviklerfiler | Windows Content Indexer Catalog File | Microsoft Windows | Microsoft Corporation |
| .CK | Ge Wang | Utviklerfiler | ChucK Source Code | ChucK | Ge Wang |
| .CKBX | Cricket Technology | Utviklerfiler | Cricket Audio XML Bank Description File | Cricket audio | Cricket Technology |
| .CKM | Bethesda Softworks | Utviklerfiler | Creation Kit Macro | The Elder Scrolls V: Skyrim | Bethesda Softworks |
| .CLA | Oracle Corporation | Utviklerfiler | Java Class Data | Java | Oracle Corporation |
| .CLASS | Oracle Corporation | Utviklerfiler | Java Class File | Eclipse IDE for Java Developers | The Eclipse Foundation |
| .CLJ | Open Source | Utviklerfiler | Clojure Source Code | Clojure | Open Source |
| .CLU | Revolution Software | Utviklerfiler | Broken Sword 2 Dialogue Data | Broken Sword 2 | Revolution Software |
| .CLW | Microsoft Corporation | Utviklerfiler | Visual C++ ClassWizard File | Microsoft Visual C++ | Microsoft Corporation |
| .CMA | Pierre Chambart, Jean-Christophe FILLIATRE and Sylvain Le Gall | Utviklerfiler | Applix Builder File | Camomile (Library File) | Pierre Chambart, Jean-Christophe FILLIATRE and Sylvain Le Gall |
| .CMAKE | Kitware, Inc. | Utviklerfiler | CMake File | CMake | Kitware, Inc. |
| .CNT | Microsoft Corporation | Utviklerfiler | Help Contents File | Microsoft HTML Help Workshop | Microsoft Corporation |
| .COB | IBM | Utviklerfiler | COBOL Source Code File | GNU Compiler Collection (GCC) | GNU Project |
| .COD | Unknown Developer | Utviklerfiler | Compiled Source Code | Microsoft Visual Studio | Microsoft Corporation |
| .COLA | Melvin Smith | Utviklerfiler | Cola Source Code File | COLA | Melvin Smith |
| .CONFIG | Unknown Developer | Utviklerfiler | Configuration File | Microsoft Notepad | Microsoft Corporation |
| .CP | Apple | Utviklerfiler | Xcode C++ Source File | Apple Xcode | Apple |
| .CPJ | NVIDIA | Utviklerfiler | NVIDIA CUDA Project | CUDA ToolKit | NVIDIA |
| .CPP | Open Source | Utviklerfiler | C++ Source Code File | Microsoft Visual Studio | Microsoft Corporation |
| .CPZ | Terry A. Davis | Utviklerfiler | LoseThos C+ Source File | LoseThos | Terry A. Davis |
| .CR2 | Canon Inc. | Utviklerfiler | Canon Digital Camera Raw Image File | CodedColor PhotoStudio | 1Stein |
| .CR5 | Campbell Scientific | Utviklerfiler | CRBasic Source Code File | CR300-Series Dataloggers | Campbell Scientific |
| .CR7 | Campbell Scientific | Utviklerfiler | CRBasic Source Code File | CR300-Series Dataloggers | Campbell Scientific |
| .CS | Microsoft Corporation | Utviklerfiler | C# Source Code File | Notepad++ | Don Ho |
| .CSB | Corel | Utviklerfiler | Corel PHOTO-PAINT Script | Corel Photo-Paint | Corel |
| .CSC | Corel | Utviklerfiler | Corel Script File | Corel Photo-Paint | Corel |
| .CSHRC | The Open Group | Utviklerfiler | Unix Command Data | GNU Emacs | GNU Project |
| .CSI | ContentServ | Utviklerfiler | ContentServ Include File | ContentServ CS EMMS Suite | ContentServ |
| .CSIG | Open Source | Utviklerfiler | SCons Content Signature | SCons | Open Source |
| .CSN | Adobe Systems Incorporated | Utviklerfiler | Adobe Code Snippet Document | Adobe Dreamweaver | Adobe Systems Incorporated |
| .CSP | RadGs Software | Utviklerfiler | Concept Server Page | Mozilla Firefox | Mozilla |
| .CSPROJ | Microsoft Corporation | Utviklerfiler | Visual Studio C# Project | Microsoft Visual Studio | Microsoft Corporation |
| .CST | Smith Micro Software | Utviklerfiler | Manga Studio Story File | Manga Studio | Smith Micro Software |
| .CSX | Microsoft Corporation | Utviklerfiler | Visual C# Script | Notepad++ | Don Ho |
| .CTC | Microsoft Corporation | Utviklerfiler | Visual Studio Command Table Configuration | Microsoft Visual Studio | Microsoft Corporation |
| .CTL | Open Source | Utviklerfiler | StepMania SMZIP Package Description File | StepMania | Open Source |
| .CTP | Cake Software Foundation | Utviklerfiler | CakePHP Template | Adobe Dreamweaver | Adobe Systems Incorporated |
| .CTX | Microsoft Corporation | Utviklerfiler | Visual Basic Control Binary File | Microsoft Visual Studio | Microsoft Corporation |
| .CU | NVIDIA | Utviklerfiler | CUDA Source Code File | Microsoft Notepad | Microsoft Corporation |
| .CUF | Borland | Utviklerfiler | Turbo C Utilities Form Definition | Turbo C | Borland |
| .CV4 | Microsoft Corporation | Utviklerfiler | Microsoft CodeView Graphics Data | CodeView | Microsoft Corporation |
| .CWL | Open Source | Utviklerfiler | TeXstudio Completion Word List | TeXstudio | Open Source |
| .CX | OrbiTech Ltd. | Utviklerfiler | CodeMapper Script | CodeMapper | OrbiTech Ltd. |
| .CXE | Sublime HQ Pty Ltd | Utviklerfiler | Common XML Envelope Data | Microsoft Notepad | Microsoft Corporation |
| .CXP | Omron Corporation | Utviklerfiler | CX-Programmer Project File | OMRON CX-One | Omron Corporation |
| .CXT | Omron Corporation | Utviklerfiler | CX-Programmer Project Text File | OMRON CX-One | Omron Corporation |
| .CXX | Embarcadero Technologies | Utviklerfiler | C++ Main Source Code File Format | Eclipse CDT | The Eclipse Foundation |
| .CYA | Peter Güntert | Utviklerfiler | Cyana Macro | Cyana | Peter Güntert |
| .C__ | Open Source | Utviklerfiler | C++ Source Code File | Microsoft Visual Studio | Microsoft Corporation |
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