| CE | FarSide Computer Calendar File |
| CE3 | Calendar Creator 3.x 4.x Event List |
| CEG | Tempra Show Bitmap Graphic |
| CEG | Continuous Edge Graphic |
| CEL | CIMFast Event Language File |
| CEL | Autodesk Animator Graphic |
| CEL | Kiss Paper Doll File |
| CEM | Computer Graphics Meta-file |
| CER | Certificate File |
| CEX | The Currency Exchanger Rate File |
| CEX | ThumbsPlus File |
| CF | Imake Configurtion File |
| CFB | Comptons Multimedia File |
| CFC | Cold Fusion File |
| CFF | Compact Font Format |
| CFG | Configuration File |
| CFL | Corel Flowchart File |
| CFL | Microsoft Developer Studio diagram |
| CFM | Cold Fusion Template File |
| CFM | Visual dBASE Windows Custom Form |
| CFM | Corel FontMaster |
| CFN | Atari Calamus Font Data File |
| CFO | TCU Turbo C Utilities C Form Object |
| CFP | Complete Fax Portable Fax File |
| CFT | Corel Flow Template flow chart |
| CG | Guitartab Chord Groover songs (More Info) |
| CGA | Bitmap Picture |
| CGA | Ventura CGA Screen Characters |
| CGI | Common Gateway Interface Script |
| CGM | Computer Graphics Metafile |
| CH | OS/2 Configuration File |
| CH | Clipper Header |
| CH3 | Harvard Graphics for DOS 3.0 Chart |
| CH4 | Charisma 4 Presentation |
| CHA | Adobe Pagemaker Kerning Data |
| CHD | FontChameleon Font Descriptor |
| CHF | pcAnywhere Remote Control File |
| CHH | C++ Header Source Code |
| CHI | ChiWriter Document |
| CHI | Help File Index |
| CHJ | Help Composer Project |
| CHK | CHKDSK/SCANDISK Output |
| CHK | WordPerfect Temp File |
| CHL | Configuration History Log |
| CHL | Chromeleon Channel Raw Data |
| CHM | Compiled HTML File |
| CHM | Ares Font Chameleon Source Font |
| CHN | Ethnograph 3 Data File |
| CHO | Ares Font Chameleon Output Font |
| CHP | Ventura Publisher Chapter Document |
| CHQ | Microsoft HTML Help Full-text Search Index for CHM |
| CHR | Character or Font File |
| CHS | Corel Presentations Chart Style |
| CHS | ATI Radeon Video Driver File |
| CHT | Harvard Graphics Vector File |
| CHT | ChartViewer dBase Interface File |
| CHT | Cheat Machine Data File |
| CHW | Microsoft HTML Help Index |
| CIF | Ventura Chapter Information |
| CIF | Easy CD Creator Image |
| CIF | pcAnywhere Caller File |
| CIF | Ventura Converted Image File |
| CIF | Colombo Ipermedia File |
| CIL | Clip Gallery Download Package |
| CIM | Sim City File |
| CIN | Microsoft Cinemania |
| CIN | OS/2 Change Control File |
| CIP | Ghost Keylogger File |
| CIR | SuperMax E-CAD Save-File Command |
| CIS | CompuServe Mail text |
| CIT | Intergraph Scanned Image |
| CIX | TCU Turbo C Utilities Database Index |
| CK1 | iD/Apogee Commander Keen Data File (.CK1 to .CK6) |
| CKB | Borland C++ Keyboard Mapping File |
| CKP | Ingres Checkpoint File |
| CL | Generic LISP Source Code |
| CL3 | Easy CD Creator Layout File |
| CL4 | Easy CD Creator Layout File |
| CL5 | Easy CD Creator Layout File |
| CLA | Java Class File (usually .CLASS but can be shortened) |
| CLB | ICQ Contact List |
| CLB | cdrLabel Compact Disc Label |
| CLB | MS Office XP Developer Code Librarian |
| CLC | Microsoft Schedule+ 7-Habits Mission Statement |
| CLG | Disk Catalog Database |
| CLK | Corel R.A.V.E. Animation File |
| CLL | Crick Software Clicker File |
| CLM | Micrografx Picture Publisher 7 Macro |
| CLO | Cloe Image |
| CLP | Windows Clipboard File |
| CLP | Quattro Pro Clip Art |
| CLP | Clipper 5 Compiler Script |
| CLR | PhotStyler Colour Defintion |
| CLR | 1st Reader Binary Colour Screen Image |
| CLR | WinEdit Colourisation Word List |
| CLS | Visual Basic Class Module |
| CLS | C++ Class Definition |
| CLS | JavaScript Class |
| CLS | Actor Class Library |
| CLW | Microsoft Visual C++ Class Wizard |
| CLW | CLARION Database |