| .C01 | e-merge GmbH | Ficheiros de Áudio | WinAce Split Archive Part 1 File | WinAce | e-merge GmbH |
| .CA3 | Casio Computer Co., Ltd. | Ficheiros de Áudio | Casio WK-1800 Save All Data | WK-1800 | Casio Computer Co., Ltd. |
| .CAF | Apple | Ficheiros de Áudio | Apple Core Audio File | Apple QuickTime Player | Apple |
| .CAFF | Apple | Ficheiros de Áudio | Core Audio File | Apple QuickTime Player | Apple |
| .CAP | Microsoft Corporation | Ficheiros de Áudio | Network Monitor Packet Capture Data File | Microsoft Network Monitor | Microsoft Corporation |
| .CC_ | Unknown Developer | Ficheiros de Áudio | Audio Utility Midimach Compressed File | Unknown Software | Unknown Developer |
| .CD | Microsoft Corporation | Ficheiros de Áudio | Visual Studio Class Diagram | Microsoft Visual Studio | Microsoft Corporation |
| .CDA | Microsoft Corporation | Ficheiros de Áudio | CD Audio Track Shortcut | Microsoft Windows Media Player | Microsoft Corporation |
| .CDDA | Microsoft Corporation | Ficheiros de Áudio | CD Digital Audio File | Apple iTunes | Apple |
| .CDG | Open Source | Ficheiros de Áudio | Compact Disc Plus Graphics Image | Nullsoft Winamp | Nullsoft |
| .CDO | NCH Software | Ficheiros de Áudio | Crescendo Music Notation File | NCH Crescendo Music Notation Editor | NCH Software |
| .CDR | Corel | Ficheiros de Áudio | CorelDRAW Vector Image File | Adobe Illustrator CC | Adobe Systems Incorporated |
| .CEL | Affymetrix | Ficheiros de Áudio | Affymetrix Probe Results File | The MathWorks MATLAB | MathWorks |
| .CF1 | Würth Online World GmbH | Ficheiros de Áudio | WOW! Data | WOW! | Würth Online World GmbH |
| .CFA | Frontline | Ficheiros de Áudio | ComProbe Analyzer Capture File | Frontline ComProbe Analysis System | Frontline |
| .CKB | Cricket Technology | Ficheiros de Áudio | Cricket Audio Bank File | Cricket audio | Cricket Technology |
| .CKF | Casio Computer Co., Ltd. | Ficheiros de Áudio | Casio Keyboard File | Casio Data Manager | Casio Computer Co., Ltd. |
| .CL3 | Roxio | Ficheiros de Áudio | Easy CD Creator CD Layout | Roxio Creator NXT Pro 5 | Roxio |
| .CMF | Creative Technology Ltd. | Ficheiros de Áudio | Creative Music Format | Nullsoft Winamp | Nullsoft |
| .CMP | Microsoft Corporation | Ficheiros de Áudio | Windows Connection Manager Profile | Microsoft Windows Server 2016 | Microsoft Corporation |
| .COPY | Sony Mobile Communications | Ficheiros de Áudio | Sony Ericsson Protected Content File | Sony Ericsson Mobile Phones | Sony Mobile Communications |
| .CPR | Steinberg | Ficheiros de Áudio | Cubase Project | Steinberg Cubase | Steinberg |
| .CPT | Corel | Ficheiros de Áudio | Corel Photo-Paint Image | Corel Presentations X8 | Corel |
| .CS3 | Casio Computer Co., Ltd. | Ficheiros de Áudio | Casio WK-1800 Keyboard Output File | WK-1800 | Casio Computer Co., Ltd. |
| .CSH | Adobe Systems Incorporated | Ficheiros de Áudio | Photoshop Custom Shapes File | Adobe Photoshop Elements | Adobe Systems Incorporated |
| .CTS | Reallusion, Inc. | Ficheiros de Áudio | CrazyTalk Script File | CrazyTalk | Reallusion, Inc. |
| .CWP | Cakewalk, Inc. | Ficheiros de Áudio | Cakewalk SONAR Project | Cakewalk SONAR | Cakewalk, Inc. |
| .CWS | ChordWizard Software Pty Ltd | Ficheiros de Áudio | ChordWizard Songtrix Song | ChordWizard Songtrix | ChordWizard Software Pty Ltd |
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