| csf | Informative Graphics Content Sealed Format Document |
| csg | OpenSCAD Constructive Solid Geometry Model |
| css | Cascading Style Sheets |
| cst | Adobe Director Cast |
| csv | Comma-Separated Values |
| ct2 | CTRAN/W Graphical Layout |
| ctb | Color-dependent Plot Style Table |
| cte | Classical Text Editor Document |
| ctex | Chinese TeX Document |
| ctf | WhereIsIt Catalog File |
| ctg | WhereIsIt Catalog Group File |
| ctm | WhereIsIt Template File |
| ctp | CardExchange 7 Card Template |
| ctx | Creativyst Table eXchange Document |
| cust | QuarkXPress for Mac Custom Data |
| cvw | Actuate Analytics Cube Report |
| cvw | CaseView Document |
| cw | CardWorks Template |
| cw3 | ClarisWorks 3 Document |
| cwb | Cakewalk Sonar Bundle |
| cwe | Crossword Express Document |
| cwf | CorelDraw Workspace |
| cwgr | ClarisWorks Drawing Document |
| cwk | ClarisWorks Document |
| cwn | Cifraweb Editor Notation Document |
| cwpt | ClarisWorks Painting Drawing |
| cws | ChordWizard Songtrix Song |
| cws | ClarisWorks Template |
| cwss | ClarisWorks Spreadsheet Document |
| cwt | ClarisWorks Texture |
| cww | CU-Writer Document |
| cwwp | ClarisWorks Word Processor Document |
| cwz | Circuit Wizard Document |
| cxbml | BML W5 Model |
| cxl | Content Extraction Language Document |