| Extension | File Description |
| .CKA | Uncommon Files |
| .CKB | Uncommon Files |
| .CKC | Uncommon Files |
| .CKD | CAD Files |
| .CKE | Uncommon Files |
| .CKF | Uncommon Files |
| .CKG | Uncommon Files |
| .CKH | Uncommon Files |
| .CKI | Uncommon Files |
| .CKJ | Uncommon Files |
| .CKK | Uncommon Files |
| .CKL | Uncommon Files |
| .CKM | Uncommon Files |
| .CKN | Uncommon Files |
| .CKO | Uncommon Files |
| .CKP | Uncommon Files |
| .CKQ | Uncommon Files |
| .CKR | Uncommon Files |
| .CKS | Uncommon Files |
| .CKT | Data Files |
| .CKU | Uncommon Files |
| .CKV | Uncommon Files |
| .CKW | Uncommon Files |
| .CKX | Uncommon Files |
| .CKY | Uncommon Files |
| .CKZ | Uncommon Files |
| .CL | Misc Files |
| .CL0 | Uncommon Files |
| .CL1 | Uncommon Files |
| .CL2 | Uncommon Files |
| .CL3 | Uncommon Files |
| .CL4 | Data Files |
| .CL5 | Disk Image Files |
| .CL6 | Uncommon Files |
| .CL7 | Uncommon Files |
| .CL8 | Uncommon Files |
| .CL9 | Uncommon Files |
| .CLA | Uncommon Files |
| .CLAP | Uncommon Files |
| .CLASS | Developer Files |
| .CLB | Data Files |
| .CLBX | Uncommon Files |
| .CLC | Uncommon Files |
| .CLD | Page Layout Files |
| .CLDLYR | Uncommon Files |
| .CLE | Uncommon Files |
| .CLEAN | Uncommon Files |
| .CLEANER | Uncommon Files |
| .CLEAR | Uncommon Files |
| .CLEARANCE | Uncommon Files |
| .CLF | Uncommon Files |
| .CLG | Settings Files |
| .CLH | Uncommon Files |
| .CLI | Uncommon Files |
| .CLICK | Uncommon Files |
| .CLIP | Uncommon Files |
| .CLIP1 | Uncommon Files |
| .CLIP2 | Uncommon Files |
| .CLJ | Uncommon Files |
| .CLK | Data Files |
| .CLKK | Misc Files |
| .CLKP | Data Files |
| .CLKT | Misc Files |
| .CLKW | Misc Files |
| .CLKX | Misc Files |
| .CLL | Uncommon Files |
| .CLM | Data Files |
| .CLMOV | Uncommon Files |
| .CLN | Uncommon Files |
| .CLO | Uncommon Files |
| .CLOCK | Uncommon Files |
| .CLOE | Uncommon Files |
| .CLOG | Uncommon Files |
| .CLOSED | Uncommon Files |
| .CLOUD | Uncommon Files |
| Extension | File Description |
| .CLP | Data Files |
| .CLPI | Video Files |
| .CLQ | Uncommon Files |
| .CLR | Settings Files |
| .CLS | Developer Files |
| .CLT | Page Layout Files |
| .CLU | Uncommon Files |
| .CLUB | Uncommon Files |
| .CLUBS | Uncommon Files |
| .CLV | Uncommon Files |
| .CLW | Developer Files |
| .CLX | Encoded Files |
| .CLY | Uncommon Files |
| .CLZ | Uncommon Files |
| .CL_ | Uncommon Files |
| .CM | Game Files |
| .CM0 | Uncommon Files |
| .CM1 | Uncommon Files |
| .CM2 | 3D Image Files |
| .CM3 | Uncommon Files |
| .CM4 | Uncommon Files |
| .CM5 | Uncommon Files |
| .CM6 | Uncommon Files |
| .CM7 | Uncommon Files |
| .CM8 | Uncommon Files |
| .CM9 | Uncommon Files |
| .CMA | Uncommon Files |
| .CMAP | Data Files |
| .CMB | Uncommon Files |
| .CMBL | Data Files |
| .CMBX | Uncommon Files |
| .CMC | Uncommon Files |
| .CMD | Executable Files |
| .CMD5 | Uncommon Files |
| .CMDF | Uncommon Files |
| .CMDR | Uncommon Files |
| .CME | Game Files |
| .CMF | 3D Image Files |
| .CMG | Uncommon Files |
| .CMH | Uncommon Files |
| .CMI | Uncommon Files |
| .CMJ | Uncommon Files |
| .CMK | Uncommon Files |
| .CML | Data Files |
| .CMM | Misc Files |
| .CMMF | Uncommon Files |
| .CMMP | Video Files |
| .CMMTPL | Video Files |
| .CMN | Uncommon Files |
| .CMO | Uncommon Files |
| .CMP | Settings Files |
| .CMPRB | Uncommon Files |
| .CMPROJ | Video Files |
| .CMPT | Uncommon Files |
| .CMQ | Uncommon Files |
| .CMR | Uncommon Files |
| .CMRBK | Uncommon Files |
| .CMRT | Uncommon Files |
| .CMS | Web Files |
| .CMT | Uncommon Files |
| .CMTD | Uncommon Files |
| .CMU | Uncommon Files |
| .CMUWM | Uncommon Files |
| .CMV | Uncommon Files |
| .CMW | Uncommon Files |
| .CMX | Vector Image Files |
| .CMXA | Uncommon Files |
| .CMY | Uncommon Files |
| .CMYK | Uncommon Files |
| .CMZ | Uncommon Files |
| .CN | Uncommon Files |
| .CN0 | Uncommon Files |
| .CN1 | Uncommon Files |
| .CN2 | Uncommon Files |
| .CN3 | Uncommon Files |
