| Extension | File Description |
| .COSMO3 | Uncommon Files |
| .COSMO4 | Uncommon Files |
| .COSMO5 | Uncommon Files |
| .COSTS | Uncommon Files |
| .COT | Uncommon Files |
| .COU | Uncommon Files |
| .COUNT | Uncommon Files |
| .COUNTER | Uncommon Files |
| .COV | Page Layout Files |
| .COW | Uncommon Files |
| .COX | Plugin Files |
| .COY | Uncommon Files |
| .COZ | Uncommon Files |
| .CP | Developer Files |
| .CP0 | Uncommon Files |
| .CP1 | Uncommon Files |
| .CP2 | Uncommon Files |
| .CP3 | Uncommon Files |
| .CP4 | Uncommon Files |
| .CP5 | Uncommon Files |
| .CP6 | Uncommon Files |
| .CP7 | Uncommon Files |
| .CP8 | Uncommon Files |
| .CP9 | Uncommon Files |
| .CP? | Misc Files |
| .CPA | CAD Files |
| .CPAN | Uncommon Files |
| .CPAO | Uncommon Files |
| .CPB | Uncommon Files |
| .CPC | Raster Image Files |
| .CPD | Raster Image Files |
| .CPE | Page Layout Files |
| .CPF | Settings Files |
| .CPG | Web Files |
| .CPGZ | Compressed Files |
| .CPH | Page Layout Files |
| .CPI | System Files |
| .CPICS | Uncommon Files |
| .CPIO | Encoded Files |
| .CPJ | Uncommon Files |
| .CPK | Game Files |
| .CPL | System Files |
| .CPM | Uncommon Files |
| .CPN | Game Files |
| .CPO | Uncommon Files |
| .CPP | Developer Files |
| .CPQ | System Files |
| .CPR | System Files |
| .CPS | Raster Image Files |
| .CPT | Encoded Files |
| .CPT6 | Uncommon Files |
| .CPTHEME | Uncommon Files |
| .CPU | Uncommon Files |
| .CPV | Uncommon Files |
| .CPW | Uncommon Files |
| .CPX | Game Files |
| .CPY | Page Layout Files |
| .CPZ | Uncommon Files |
| .CQ | Uncommon Files |
| .CQ0 | Uncommon Files |
| .CQ1 | Uncommon Files |
| .CQ2 | Uncommon Files |
| .CQ3 | Uncommon Files |
| .CQ4 | Uncommon Files |
| .CQ5 | Uncommon Files |
| .CQ6 | Uncommon Files |
| .CQ7 | Uncommon Files |
| .CQ8 | Uncommon Files |
| .CQ9 | Uncommon Files |
| .CQA | Uncommon Files |
| .CQB | Uncommon Files |
| .CQC | Uncommon Files |
| .CQD | Uncommon Files |
| .CQE | Uncommon Files |
| .CQF | Uncommon Files |
| Extension | File Description |
| .CQG | Uncommon Files |
| .CQH | Uncommon Files |
| .CQI | Uncommon Files |
| .CQJ | Uncommon Files |
| .CQK | Uncommon Files |
| .CQL | Uncommon Files |
| .CQM | Uncommon Files |
| .CQN | Uncommon Files |
| .CQO | Uncommon Files |
| .CQP | Uncommon Files |
| .CQQ | Uncommon Files |
| .CQR | Uncommon Files |
| .CQS | Uncommon Files |
| .CQT | Uncommon Files |
| .CQU | Uncommon Files |
| .CQV | Uncommon Files |
| .CQW | Uncommon Files |
| .CQX | Uncommon Files |
| .CQY | Uncommon Files |
| .CQZ | Uncommon Files |
| .CR | Uncommon Files |
| .CR$ | Uncommon Files |
| .CR0 | Uncommon Files |
| .CR1 | Uncommon Files |
| .CR2 | Raster Image Files |
| .CR3 | Uncommon Files |
| .CR4 | Uncommon Files |
| .CR5 | Uncommon Files |
| .CR6 | Uncommon Files |
| .CR7 | Uncommon Files |
| .CR8 | Uncommon Files |
| .CR9 | Uncommon Files |
| .CRA | Uncommon Files |
| .CRACK | Uncommon Files |
| .CRACKING | Uncommon Files |
| .CRACKPOTY | Uncommon Files |
| .CRACKZBYMA | Uncommon Files |
| .CRAM | Uncommon Files |
| .CRASH | System Files |
| .CRASH2 | Uncommon Files |
| .CRATE | Uncommon Files |
| .CRAW | Uncommon Files |
| .CRAZE | Uncommon Files |
| .CRAZY | Uncommon Files |
| .CRB | Uncommon Files |
| .CRC | Misc Files |
| .CRC16 | Uncommon Files |
| .CRD | Misc Files |
| .CRDEL | Uncommon Files |
| .CRDOWNLOAD | Web Files |
| .CRE | Uncommon Files |
| .CREATOR | Uncommon Files |
| .CREDITS | Uncommon Files |
| .CREG | Uncommon Files |
| .CRF | 3D Image Files |
| .CRG | Uncommon Files |
| .CRH | Uncommon Files |
| .CRI | Uncommon Files |
| .CRJ | Uncommon Files |
| .CRK | Uncommon Files |
| .CRL | Web Files |
| .CRLD | Uncommon Files |
| .CRM | Uncommon Files |
| .CRN | Uncommon Files |
| .CRO | Uncommon Files |
| .CRONTAB | Uncommon Files |
| .CROPS | Uncommon Files |
| .CROSS | Uncommon Files |
| .CROWN | Uncommon Files |
| .CRP | Uncommon Files |
| .CRQ | Uncommon Files |
| .CRR | Uncommon Files |
| .CRS | Game Files |
| .CRT | Web Files |
| .CRU | Uncommon Files |
