| .CAMP | Microsoft Corporation | Indstillingsfiler | WCS Color Appearance Model Profile File | Microsoft Windows | Microsoft Corporation |
| .CASE | Bohemian Coding | Indstillingsfiler | SlipCover Case File | SlipCover | Bohemian Coding |
| .CCF | Interscape | Indstillingsfiler | CryptLoad Container File | CryptLoad | CryptLoad |
| .CCM | Clickteam | Indstillingsfiler | Multimedia Fusion Custom Menu Data | Clickteam Fusion 2.5 | Clickteam |
| .CDF | Wolfram Research | Indstillingsfiler | Computable Document Format File | Wolfram Research CDF Player | Wolfram Research |
| .CDT | Sony | Indstillingsfiler | CD-Text File | IsoBuster | Smart Projects |
| .CEX | Dassault Systèmes | Indstillingsfiler | SolidWorks Enterprise PDM Vault Export File | Dassault Systemes SolidWorks | Dassault Systèmes |
| .CF | Proofpoint, Inc. | Indstillingsfiler | Sendmail Configuration File | Apache OpenOffice | Apache Software Foundation |
| .CGR | Dassault Systèmes | Indstillingsfiler | CATIA Graphical Representation File | CATIA | Dassault Systèmes |
| .CHA | Snak Software | Indstillingsfiler | IRC Chat Configuration File | Visual IRC | Adrian Cable and Jesse McGrew |
| .CHK | Sophos | Indstillingsfiler | InterCheck Checksum Database | Sophos | Sophos |
| .CHL | Leadtek Research | Indstillingsfiler | WinFast PVR2 Channel List | Leadtek Research WinFast PVR2 | Leadtek Research |
| .CHX | Autodesk, Inc. | Indstillingsfiler | AutoCAD Standards Check File | Autodesk AutoCAD Ecscad | Autodesk, Inc. |
| .CIK | Corel | Indstillingsfiler | Corel Graphics 10 Custom Dual Tone File | CorelDRAW Graphics Suite | Corel |
| .CIS | VicTech Software | Indstillingsfiler | CheckInbox Settings File | VicTech Software CheckInbox | VicTech Software |
| .CKS | Microsoft Corporation | Indstillingsfiler | Microsoft Windows CE Image Info Data | Microsoft Windows CE Embedded | Microsoft Corporation |
| .CLR | Adobe Systems Incorporated | Indstillingsfiler | Animate Color Set | Adobe Animate CC 2017 | Adobe Systems Incorporated |
| .CLV | Yamaha Corporation | Indstillingsfiler | Yamaha Cool Voices Data | Yamaha SoundVQ Player | Yamaha Corporation |
| .CLY | Corel | Indstillingsfiler | CorelDRAW Custom Layout | CorelDRAW Graphics Suite | Corel |
| .CM | Rockstar Games | Indstillingsfiler | CLEO Custom Mission | Sanny Builder | Open Source |
| .CMB | Jeffrey C. Johnson | Indstillingsfiler | Xtree For Windows Button Bar | ZTreeWin | Zedtek Inc. |
| .CMP | Microsoft Corporation | Indstillingsfiler | Windows Connection Manager Profile | Microsoft Windows Server 2016 | Microsoft Corporation |
| .CNF | MySQL AB | Indstillingsfiler | MySQL Configuration File | MySQL | Oracle Corporation |
| .CNM | David Harris | Indstillingsfiler | Pegasus Mail New Message Template File | CaseMap | LexisNexis |
| .COL | Open Source | Indstillingsfiler | Bibexcel File | BibExcel | Open Source |
| .CONF | Unknown Developer | Indstillingsfiler | Generic Configuration File | Microsoft Notepad | Microsoft Corporation |
| .CONFIGURE | Open Source | Indstillingsfiler | Bash Data | Linux | Open Source |
| .CONT | Panasonic Corporation | Indstillingsfiler | Panasonic Camcorder Metadata | Panasonic HD Writer AE | Panasonic Corporation |
| .COP | Cisco Systems | Indstillingsfiler | CISCO Options Package Settings | Unknown Software | Unknown Developer |
| .COS | Phase One | Indstillingsfiler | Capture One Settings File | Capture One | Phase One |
| .CPF | IBM | Indstillingsfiler | Cognos Project File | IBM Cognos Business Intelligence | IBM |
| .CPL | Microsoft Corporation | Indstillingsfiler | Windows Control Panel Item | Microsoft Windows | Microsoft Corporation |
| .CPM | Cisco Systems | Indstillingsfiler | Cisco Secure Policy Manager Settings | Cisco Secure Policy Manager | Cisco Systems |
| .CPR | Steinberg | Indstillingsfiler | Cubase Project | Steinberg Cubase | Steinberg |
| .CPS | Interscape | Indstillingsfiler | The Powder Toy Save File | The Powder Toy | Interscape |
| .CPX | Oracle Corporation | Indstillingsfiler | Oracle ADF Binding Context File | Oracle JDeveloper | Oracle Corporation |
| .CRW | Canon Inc. | Indstillingsfiler | Canon Raw CIFF Image File | MacPhun ColorStrokes | Macphun |
| .CSA | Agilent Technologies | Indstillingsfiler | PNA Code Calset File | PNA Code | Agilent Technologies |
| .CSF | Intergraph Corporation | Indstillingsfiler | GeoMedia Coordinate System File | Intergraph GeoMedia | Hexagon Geospatial |
| .CSK | Apple | Indstillingsfiler | ClarisWorks Data | Apple AppleWorks | Apple |
| .CST | Smith Micro Software | Indstillingsfiler | Manga Studio Story File | Manga Studio | Smith Micro Software |
| .CSW | Corel | Indstillingsfiler | Corel WordPerfect Setup Information Data | Corel WordPerfect | Corel |
| .CTB | Autodesk, Inc. | Indstillingsfiler | AutoCAD Color-Based Plot Style File | Autodesk AutoCAD | Autodesk, Inc. |
| .CUS | Autodesk, Inc. | Indstillingsfiler | AutoCAD Custom Dictionary File | Microsoft Notepad | Microsoft Corporation |
| .CVA | Hewlett-Packard | Indstillingsfiler | HP SSM Information File | HP System Software Manager (SSM) | Hewlett-Packard |
| .CWF | Corel Corporation | Indstillingsfiler | CorelDRAW Workspace File | CorelDRAW Graphics Suite | Corel |
| .CYBERDUCKLICENSE | Open Source | Indstillingsfiler | Cyberduck Donation Key | Cyberduck | Open Source |
| .CYBERDUCKPROFILE | Open Source | Indstillingsfiler | Cyberduck Connection Profile | Cyberduck | Open Source |
| .CYM | Open Source | Indstillingsfiler | AdPlug Callus OPL Register Logs | AdPlug | Open Source |
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