| Extension | File Description |
| .CRUNCH | Uncommon Files |
| .CRUNCHER | Uncommon Files |
| .CRV | CAD Files |
| .CRW | Raster Image Files |
| .CRX | Plugin Files |
| .CRY | Data Files |
| .CRYPTOMITE | Uncommon Files |
| .CRYPTONOTE | Data Files |
| .CRYPTRA | Encoded Files |
| .CRYPTX | Uncommon Files |
| .CRYSISJMSF | Game Files |
| .CRYSTALHAM | Uncommon Files |
| .CRZ | 3D Image Files |
| .CS | Game Files |
| .CS-CNF | Uncommon Files |
| .CS0 | Uncommon Files |
| .CS1 | Uncommon Files |
| .CS2 | Uncommon Files |
| .CS3 | Uncommon Files |
| .CS4 | Uncommon Files |
| .CS5 | Uncommon Files |
| .CS6 | Uncommon Files |
| .CS7 | Uncommon Files |
| .CS8 | Uncommon Files |
| .CS9 | Uncommon Files |
| .CSA | Data Files |
| .CSB | Uncommon Files |
| .CSC | Uncommon Files |
| .CSD | 3D Image Files |
| .CSE | Uncommon Files |
| .CSF | Raster Image Files |
| .CSFDB | Uncommon Files |
| .CSG | Uncommon Files |
| .CSH | Audio Files |
| .CSHRC | Uncommon Files |
| .CSI | Developer Files |
| .CSJ | Uncommon Files |
| .CSK | Uncommon Files |
| .CSL | Data Files |
| .CSLM | Uncommon Files |
| .CSM | 3D Image Files |
| .CSML | Uncommon Files |
| .CSN | Developer Files |
| .CSO | Disk Image Files |
| .CSP | Web Files |
| .CSPROJ | Developer Files |
| .CSQ | Uncommon Files |
| .CSR | Web Files |
| .CSS | Web Files |
| .CSS1 | Uncommon Files |
| .CST | Page Layout Files |
| .CSU | Uncommon Files |
| .CSUP | Uncommon Files |
| .CSV | Data Files |
| .CSVENX | Uncommon Files |
| .CSW | Uncommon Files |
| .CSX | Uncommon Files |
| .CSY | Vector Image Files |
| .CSZ | Uncommon Files |
| .CS_ | Uncommon Files |
| .CT | Game Files |
| .CT0 | Uncommon Files |
| .CT1 | Uncommon Files |
| .CT2 | Uncommon Files |
| .CT3 | Uncommon Files |
| .CT4 | Uncommon Files |
| .CT5 | Uncommon Files |
| .CT6 | Uncommon Files |
| .CT7 | Uncommon Files |
| .CT8 | Uncommon Files |
| .CT9 | Uncommon Files |
| .CTA | Uncommon Files |
| .CTAB | Uncommon Files |
| .CTB | Settings Files |
| .CTC | Uncommon Files |
| Extension | File Description |
| .CTD | Uncommon Files |
| .CTE | Uncommon Files |
| .CTF | Misc Files |
| .CTFSYS | Uncommon Files |
| .CTG | Misc Files |
| .CTH | Uncommon Files |
| .CTI | Uncommon Files |
| .CTJ | Uncommon Files |
| .CTK | Uncommon Files |
| .CTL | Developer Files |
| .CTM | Data Files |
| .CTN | Uncommon Files |
| .CTO | Uncommon Files |
| .CTP | Developer Files |
| .CTQ | Uncommon Files |
| .CTR | Uncommon Files |
| .CTRL | Uncommon Files |
| .CTS | Uncommon Files |
| .CTT | Data Files |
| .CTU | Uncommon Files |
| .CTV | Data Files |
| .CTW | Uncommon Files |
| .CTX | Developer Files |
| .CTY | Game Files |
| .CTZ | Uncommon Files |
| .CU | Developer Files |
| .CU0 | Uncommon Files |
| .CU1 | Uncommon Files |
| .CU2 | Uncommon Files |
| .CU3 | Uncommon Files |
| .CU4 | Uncommon Files |
| .CU5 | Uncommon Files |
| .CU6 | Uncommon Files |
| .CU7 | Uncommon Files |
| .CU8 | Uncommon Files |
| .CU9 | Uncommon Files |
| .CUA | Uncommon Files |
| .CUB | Data Files |
| .CUBE | Uncommon Files |
| .CUBI | Uncommon Files |
| .CUC | Uncommon Files |
| .CUD | Uncommon Files |
| .CUE | Disk Image Files |
| .CUF | Uncommon Files |
| .CUG | Uncommon Files |
| .CUH | Uncommon Files |
| .CUI | Uncommon Files |
| .CUJ | Uncommon Files |
| .CUK | Uncommon Files |
| .CUL | Misc Files |
| .CUM | Uncommon Files |
| .CUN | Uncommon Files |
| .CUO | Uncommon Files |
| .CUP | Uncommon Files |
| .CUQ | Uncommon Files |
| .CUR | System Files |
| .CUREXSCHEM | Uncommon Files |
| .CURL | Uncommon Files |
| .CURSOR | Uncommon Files |
| .CURV | Uncommon Files |
| .CURVE | Uncommon Files |
| .CURXPTHEME | Data Files |
| .CUS | Settings Files |
| .CUSTOM | Uncommon Files |
| .CUT | Raster Image Files |
| .CUTLIST | Uncommon Files |
| .CUU | Uncommon Files |
| .CUV | Uncommon Files |
| .CUW | Uncommon Files |
| .CUX | Uncommon Files |
| .CUY | Uncommon Files |
| .CUZ | Uncommon Files |
| .CU_ | Uncommon Files |
| .CV | Uncommon Files |
| .CV0 | Uncommon Files |
