| .CKN | Disk Doctor Labs Inc. | Arquivos de dados | Disk Doctors License Log | Unknown Software | Unknown Developer |
| .CKT | Altium | Arquivos de dados | CircuitMaker File | Altium Designer | Altium |
| .CKY | DragonMinded.com | Arquivos de dados | DSOrganize Data | DSOrganize | DragonMinded.com |
| .CL3 | Roxio | Arquivos de dados | Easy CD Creator CD Layout | Roxio Creator NXT Pro 5 | Roxio |
| .CL4 | Roxio | Arquivos de dados | Easy CD Creator 4 Project File | Roxio Easy CD Creator | Roxio |
| .CLAP | Unknown Developer | Arquivos de dados | Unknown Apple II File. (found On Golden Orchard Apple II CD Rom) | Atom | GitHub, Inc. |
| .CLB | Microsoft Corporation | Arquivos de dados | COM+ Catalog File | Microsoft COM+ | Microsoft Corporation |
| .CLC | Microsoft Corporation | Arquivos de dados | Microsoft Schedule+ 7 Habits Mission Statement Data | Microsoft Schedule Plus | Microsoft Corporation |
| .CLE | Moon Valley Software, Inc. | Arquivos de dados | Icon Lock-iT Locked File Indicator | Icon Lock-iT | Moon Valley Software, Inc. |
| .CLEANER | Unknown Developer | Arquivos de dados | Unknown Apple II File. (found On Golden Orchard Apple II CD Rom) | Atom | GitHub, Inc. |
| .CLG | Microsoft Corporation | Arquivos de dados | Windows Catalog File | Microsoft Windows | Microsoft Corporation |
| .CLK | Corel | Arquivos de dados | Corel R.A.V.E Project File | CorelDRAW Graphics Suite | Corel |
| .CLKP | Crick Software | Arquivos de dados | Clicker Palette | Crick software clicker | Crick Software |
| .CLL | Crick Software | Arquivos de dados | Crick Software Clicker Data | Crick software clicker | Crick Software |
| .CLM | YMAX | Arquivos de dados | MagicJack Call Log File | YMAX magicjack | YMAX |
| .CLO | Pierre-Emmanuel Gougelet | Arquivos de dados | Cloe Ray-Tracer Image | XnView MP | XnSoft |
| .CLOG | SpreadMaster | Arquivos de dados | SpreadMaster Client Log File | Unknown Software | Unknown Developer |
| .CLONEDVD | Elaborate Bytes | Arquivos de dados | CloneDVD Registration Data | elby CloneDVD | Elaborate Bytes |
| .CLOSED | Unknown Developer | Arquivos de dados | Unknown Apple II File. (found On Golden Orchard Apple II CD Rom) | Atom | GitHub, Inc. |
| .CLP | Reallusion, Inc. | Arquivos de dados | CrazyTalk Clip File | CrazyTalk | Reallusion, Inc. |
| .CLT | Clarity Legal | Arquivos de dados | Clarity Legal Transcript File | Clarity Legal Viewer | Clarity Legal |
| .CLU | Revolution Software | Arquivos de dados | Broken Sword 2 Dialogue Data | Broken Sword 2 | Revolution Software |
| .CLV | Yamaha Corporation | Arquivos de dados | Yamaha Cool Voices Data | Yamaha SoundVQ Player | Yamaha Corporation |
| .CLW | Microsoft Corporation | Arquivos de dados | Visual C++ ClassWizard File | Microsoft Visual C++ | Microsoft Corporation |
| .CLX | IBM | Arquivos de dados | Rational XDE | Rational XDE | IBM |
| .CLY | Corel | Arquivos de dados | CorelDRAW Custom Layout | CorelDRAW Graphics Suite | Corel |
| .CM5 | Sci-Ed Software | Arquivos de dados | Clone Manager File | SnapGene | GSL Biotech LLC |
| .CM6 | LexisNexis | Arquivos de dados | CaseMap Version 6.x Case Analysis File | CaseMap | LexisNexis |
| .CMAP | Institute for Human and Machine Cognition (IHMC) | Arquivos de dados | CmapTools Concept Map File | CampTools | Institute for Human and Machine Cognition (IHMC) |
| .CMBL | Vernier Software & Technology | Arquivos de dados | Logger Pro Data File | Vernier Logger Pro | Vernier Software & Technology |
| .CMC | Bitz & Pixelz | Arquivos de dados | Comic Collector Collection Data File | Comic Collector | Bitz & Pixelz |
| .CMDB | ANSYS, Inc. | Arquivos de dados | ANSYS CFX Mesh Database | ANSYS CFX | ANSYS, Inc. |
| .CMDF | CrystalMaker Software | Arquivos de dados | CrystalMaker Data File | CrystalMaker | CrystalMaker Software |
| .CML | Unknown Developer | Arquivos de dados | Chemical Markup Language File | Avogadro | Open Source |
| .CMN | Microsoft Corporation | Arquivos de dados | Systems Management Server (SMS) Update | Microsoft Systems Management Server | Microsoft Corporation |
| .CMP | Microsoft Corporation | Arquivos de dados | Windows Connection Manager Profile | Microsoft Windows Server 2016 | Microsoft Corporation |
| .CMR | CMA Coach | Arquivos de dados | Coach Results File | CMA Coach | CMA Coach |
| .CMRBK | LexisNexis | Arquivos de dados | CaseMap ReportBook Definition File | CaseMap | LexisNexis |
| .CMS | Opera Software | Arquivos de dados | Content Management System Web Page File | Safari | Apple |
| .CMY | Corel Corporation | Arquivos de dados | CorelDRAW Custom File | CorelDRAW Graphics Suite | Corel |
| .CN | Procedimientos-Uno, S.L. | Arquivos de dados | CNwin Project Data | CNwin | Procedimientos-Uno, S.L. |
| .CNA | OpEx Software LLC | Arquivos de dados | Catena Project | OpEx Catena | OpEx Software LLC |
| .CNDF | Unknown Developer | Arquivos de dados | Technomate CNDF Channel Editor Compressed Channel File | Unknown Software | Unknown Developer |
| .CNJ | Open Source | Arquivos de dados | Acharya Conjunct Data | Acharya | Open Source |
| .CNR | David Harris | Arquivos de dados | Pegasus Mail Mail Message Stored In Systemwide Folder | Pegasus Mail | David Harris |
| .CNT | Microsoft Corporation | Arquivos de dados | Help Contents File | Microsoft HTML Help Workshop | Microsoft Corporation |
| .CNX | IBM | Arquivos de dados | IBM Rational XDE Data | Rational XDE | IBM |
| .COBRA | Unknown Developer | Arquivos de dados | Unknown Apple II File. (found On Golden Orchard Apple II CD Rom) | Atom | GitHub, Inc. |
| .COF | Microchip Technology Inc. | Arquivos de dados | MPLAB COFF File | MPLAB IDE | Microchip Technology Inc. |
| .COK | Eidos Interactive | Arquivos de dados | Carmageddon Patch File | Carmageddon TDR 2000 | Torus Games |
| .COL | Open Source | Arquivos de dados | Bibexcel File | BibExcel | Open Source |
| .COLLECTION | Adobe Systems Incorporated | Arquivos de dados | Adobe Bridge Collection File | Adobe Bridge CC | Adobe Systems Incorporated |
| .COLLOQUYTRANSCRIPT | Javelin.cc | Arquivos de dados | Colloquy Chat Transcript File | Colloquy | Open Source |
| .COLORS | Richard Hughey - Kevin Karplus - Anders Krogh | Arquivos de dados | SAM Makelogo Color Data | SAM (Sequence Alignment and Modeling) | Richard Hughey - Kevin Karplus - Anders Krogh |
| .CONTACT | Microsoft Corporation | Arquivos de dados | Windows Contact File | Microsoft Windows | Microsoft Corporation |
| .CONVERTER | Apple | Arquivos de dados | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .CONVERTERX | SiMX | Arquivos de dados | SiMX TextConverter Project File | TextConverter | SiMX |
| .COOKIES | Apple | Arquivos de dados | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .COREL WORDPERFECT DICTIONARY | Corel | Arquivos de dados | Corel WordPerfect Dictionary File | Corel WordPerfect X8 | Corel |
| .CORRECT | Apple | Arquivos de dados | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .COUNTER | NetObjects | Arquivos de dados | NetObjects Fusion Components Bbscomp Message File | NetObjects Fusion | NetObjects |
| .COVERAGE | Microsoft Corporation | Arquivos de dados | Visual Studio Code Coverage Report | Microsoft Visual Studio | Microsoft Corporation |
| .COVERAGEXML | Microsoft Corporation | Arquivos de dados | Microsoft Visual Studio Code Coverage File | Microsoft Visual Studio | Microsoft Corporation |
| .CPD | Adobe Systems Incorporated | Arquivos de dados | RoboHelp Cache Project Database | Adobe RoboHelp | Adobe Systems Incorporated |
| .CPF | IBM | Arquivos de dados | Cognos Project File | IBM Cognos Business Intelligence | IBM |
| .CPI | Sony | Arquivos de dados | AVCHD Video Clip Information | Adobe Premiere Pro CC | Adobe Systems Incorporated |
| .CPK | CRI Middleware | Arquivos de dados | CRI Middleware Package | CRI Packed File Maker | CRI Middleware |
| .CPN | Microsoft Corporation | Arquivos de dados | Age Of Mythology Campaign File | Microsoft Age of Empires | Ensemble Studios |
| .CPO | Corel Corporation | Arquivos de dados | Corel Print House Data | Corel Print House | Corel |
| .CPQ | Compaq | Arquivos de dados | Compaq OEM Disc Configuration File | Microsoft Notepad | Microsoft Corporation |
| .CPW | Alexander V. Ilyin | Arquivos de dados | Online Cost Planning Service Cost Planning Work Data | Online Cost Planning Service | Alexander V. Ilyin |
| .CQP | IntelliQuilter | Arquivos de dados | CompuQuilter Pattern | CompuQuilter | IntelliQuilter |
| .CQQ | Kjartan Osmundsen | Arquivos de dados | Cool Quiz | Cool Quiz | Kjartan Osmundsen |
| .CQZ | CornEmpire Software | Arquivos de dados | Cool Quiz Quiz File | Cool Quiz for Windows | CornEmpire Software |
| .CR4 | Dr. Hsin H. Huang | Arquivos de dados | STABCAL Data File | STABCAL | Dr. Hsin H. Huang |
| .CR7 | Campbell Scientific | Arquivos de dados | CRBasic Source Code File | CR300-Series Dataloggers | Campbell Scientific |
| .CRACK | Apple | Arquivos de dados | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .CRASH | Apple | Arquivos de dados | Mac OS X Crash Log File | Apple TextEdit | Apple |
| .CRD | Open Source | Arquivos de dados | Guitar Tabs | Notepad++ | Don Ho |
| .CRF | Open Source | Arquivos de dados | Cal3D Binary Materials File | Cal3DViewer | Open Source |
| .CRN | Unknown Developer | Arquivos de dados | Tree Ring Data File | Unknown Software | Unknown Developer |
| .CRO | FAO | Arquivos de dados | CropWat Data | CropWat | FAO |
| .CRS | Open Source | Arquivos de dados | StepMania Course File | StepMania | Open Source |
| .CRTX | Microsoft Corporation | Arquivos de dados | Office 2007 Chart Template File | Microsoft Excel | Microsoft Corporation |
| .CRUNCH | Apple | Arquivos de dados | Golden Orchard Apple II CD Rom File | Apple OS X | Apple |
| .CRW | Canon Inc. | Arquivos de dados | Canon Raw CIFF Image File | MacPhun ColorStrokes | Macphun |
| .CS | Microsoft Corporation | Arquivos de dados | C# Source Code File | Notepad++ | Don Ho |
| .CSA | Agilent Technologies | Arquivos de dados | PNA Code Calset File | PNA Code | Agilent Technologies |
| .CSC | Corel | Arquivos de dados | Corel Script File | Corel Photo-Paint | Corel |
| .CSD | Valve | Arquivos de dados | Steam Game Data Backup File | Steam | Valve |
| .CSE | Macropool | Arquivos de dados | Web Research Document Package | Web Research Professional | Macropool |
| .CSHADER | Microsoft Corporation | Arquivos de dados | Microsoft Visual Studio Text Data | Microsoft Visual Studio | Microsoft Corporation |
| .CSK | Apple | Arquivos de dados | ClarisWorks Data | Apple AppleWorks | Apple |
| .CSL | Interscape | Arquivos de dados | CineStyle Color Lookup File | CineStyle Color Assist | Interscape |
| .CST | Smith Micro Software | Arquivos de dados | Manga Studio Story File | Manga Studio | Smith Micro Software |
| .CSV | Unknown Developer | Arquivos de dados | Comma Separated Values File | Microsoft Excel | Microsoft Corporation |
| .CS_ | Unknown Developer | Arquivos de dados | Creativ Compressed Sb16 Sbide File | Unknown Software | Unknown Developer |
| .CT0 | Tajima Group | Arquivos de dados | Tajima TBF Condition Data | DG/ML | Tajima Group |
| .CT1 | Microsoft Corporation | Arquivos de dados | Microsoft Systems Management Server Proposed Site Control Data | Microsoft Systems Management Server | Microsoft Corporation |
| .CT3 | Microsoft Corporation | Arquivos de dados | Microsoft Systems Management Server (SMS) Control File | Microsoft Systems Management Server | Microsoft Corporation |
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