| .CAT | Microsoft Corporation | Ficheiros Gráficos | Windows Catalog File | Microsoft Windows | Microsoft Corporation |
| .CCK | U.S. Department of Energy | Ficheiros Gráficos | COMcheck Data File | COMcheck | U.S. Department of Energy |
| .CDB | Nokia | Ficheiros Gráficos | Symbian Phonebook Database | Nokia PC Suite | Nokia |
| .CDC | Autodesk, Inc. | Ficheiros Gráficos | AutoCAD DesignCenter Preview Cache File | Autodesk AutoCAD | Autodesk, Inc. |
| .CDF | Wolfram Research | Ficheiros Gráficos | Computable Document Format File | Wolfram Research CDF Player | Wolfram Research |
| .CDU | Pierre-Emmanuel Gougelet | Ficheiros Gráficos | CDU-Paint Image Format | XnView MP | XnSoft |
| .CDW | ASCON | Ficheiros Gráficos | KOMPAS Document | ASCON KOMPAS-3D | ASCON |
| .CEG | Unknown Developer | Ficheiros Gráficos | Tempra Show Bitmap Graphic File | Unknown Software | Unknown Developer |
| .CFT | Walt Disney Animation Studios | Ficheiros Gráficos | CFast Graphics | XnView MP | XnSoft |
| .CH1 | IBM | Ficheiros Gráficos | IBM Freelance Graphics Chart File | Lotus Freelance Graphics | IBM |
| .CIF | Corel | Ficheiros Gráficos | Easy CD Creator Disk Image | IsoBuster | Smart Projects |
| .CIM | CIMEX Corporation | Ficheiros Gráficos | CimPack Design Drawing | CimPack design drawing | CIMEX Corporation |
| .CKO | Corel | Ficheiros Gráficos | Image Mask File | Corel KnockOut 2 | Corel |
| .CLO | Pierre-Emmanuel Gougelet | Ficheiros Gráficos | Cloe Ray-Tracer Image | XnView MP | XnSoft |
| .CLOUD | GOM & Company | Ficheiros Gráficos | GOM Atos Scanner Data | Rapidform Explorer (Geomagic Verify Viewer) | Rapidform, Inc. |
| .CMK | Creative Wonders | Ficheiros Gráficos | Card Shop Plus Card File | Card Shop Plus | Creative Wonders |
| .CMP | Microsoft Corporation | Ficheiros Gráficos | Windows Connection Manager Profile | Microsoft Windows Server 2016 | Microsoft Corporation |
| .CMT | Chinon Group | Ficheiros Gráficos | Chinon ES-1000 Digital Camera Image Format | Zoner Photo Studio | Zoner Software |
| .COT | Intergraph Corporation | Ficheiros Gráficos | Intergraph Image File | Intergraph SG&I software | Intergraph Corporation |
| .CP8 | Unknown Developer | Ficheiros Gráficos | CP8 256 Gray Scale Image | XnView MP | XnSoft |
| .CRF | Open Source | Ficheiros Gráficos | Cal3D Binary Materials File | Cal3DViewer | Open Source |
| .CS4 | Sinar | Ficheiros Gráficos | Sinar CaptureShop 4-shot Image File | Sinar CaptureShop | Sinar |
| .CSA | Agilent Technologies | Ficheiros Gráficos | PNA Code Calset File | PNA Code | Agilent Technologies |
| .CSE | Macropool | Ficheiros Gráficos | Web Research Document Package | Web Research Professional | Macropool |
| .CSN | Adobe Systems Incorporated | Ficheiros Gráficos | Adobe Code Snippet Document | Adobe Dreamweaver | Adobe Systems Incorporated |
| .CT2 | Geoslope | Ficheiros Gráficos | CTRAN/W Graphical Layout File | CTRAN/W | Geoslope |
| .CTM | LucasArts Entertainment Company, LLC | Ficheiros Gráficos | Star Wars Republic Commando Map File | Star Wars Republic Commando | LucasArts Entertainment Company, LLC |
| .CU1 | Computerinsel GmbH | Ficheiros Gráficos | Photoline4 Curves Curve File | Photoline | Computerinsel GmbH |
| .CURSOR | Sun Microsystems | Ficheiros Gráficos | Sun Cursor | SunOS | Sun Microsystems |
| .CWR | SAP | Ficheiros Gráficos | Crystal Reports Report | Crystal Reports | SAP |
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