| Extension | File Description |
| .CN4 | Uncommon Files |
| .CN5 | Uncommon Files |
| .CN6 | Uncommon Files |
| .CN7 | Uncommon Files |
| .CN8 | Uncommon Files |
| .CN9 | Uncommon Files |
| .CNA | Data Files |
| .CNB | Uncommon Files |
| .CNC | CAD Files |
| .CNC3REPLAY | Uncommon Files |
| .CND | Uncommon Files |
| .CNDF | Uncommon Files |
| .CNE | Uncommon Files |
| .CNF | Settings Files |
| .CNG | Uncommon Files |
| .CNH | Uncommon Files |
| .CNI | Uncommon Files |
| .CNJ | Uncommon Files |
| .CNK | Uncommon Files |
| .CNL | Uncommon Files |
| .CNM | Uncommon Files |
| .CNN | Uncommon Files |
| .CNO | Uncommon Files |
| .CNP | Uncommon Files |
| .CNQ | Uncommon Files |
| .CNR | Uncommon Files |
| .CNREG | Uncommon Files |
| .CNREP | Uncommon Files |
| .CNS | Game Files |
| .CNT | System Files |
| .CNU | Uncommon Files |
| .CNV | Vector Image Files |
| .CNW | Uncommon Files |
| .CNX | Uncommon Files |
| .CNY | Uncommon Files |
| .CNZ | Uncommon Files |
| .CN_ | Uncommon Files |
| .CO | Uncommon Files |
| .CO$ | Uncommon Files |
| .CO0 | Uncommon Files |
| .CO1 | Uncommon Files |
| .CO2 | Uncommon Files |
| .CO3 | Uncommon Files |
| .CO4 | Uncommon Files |
| .CO5 | Uncommon Files |
| .CO6 | Uncommon Files |
| .CO7 | Uncommon Files |
| .CO8 | Uncommon Files |
| .CO9 | Uncommon Files |
| .COA | Uncommon Files |
| .COB | Developer Files |
| .COBRA | Uncommon Files |
| .COC | Uncommon Files |
| .COCO | Uncommon Files |
| .COD | Text Files |
| .CODE | Uncommon Files |
| .CODE0 | Uncommon Files |
| .CODE1 | Uncommon Files |
| .CODE2 | Uncommon Files |
| .CODE3 | Uncommon Files |
| .CODE4 | Uncommon Files |
| .CODEC | Uncommon Files |
| .CODES | Uncommon Files |
| .COE | Uncommon Files |
| .COF | Executable Files |
| .COFFEE | Executable Files |
| .COG | Uncommon Files |
| .COH | Uncommon Files |
| .COI | Uncommon Files |
| .COJ | Uncommon Files |
| .COK | Uncommon Files |
| .COKE | Uncommon Files |
| .COL | Data Files |
| .COLA | Uncommon Files |
| .COLLAPSE | Uncommon Files |
| Extension | File Description |
| .COLLECTION | Data Files |
| .COLLOQUYTR | Uncommon Files |
| .COLOGNELA | Uncommon Files |
| .COLOR | Uncommon Files |
| .COLOR2 | Uncommon Files |
| .COLORS | Uncommon Files |
| .COM | Executable Files |
| .COM2 | Uncommon Files |
| .COMBAT | Uncommon Files |
| .COMFYCAKES | Game Files |
| .COMICSCART | Uncommon Files |
| .COMING | Uncommon Files |
| .COMMANDLIN | Uncommon Files |
| .COMMANDS | Uncommon Files |
| .COMMANDS2 | Uncommon Files |
| .COMMENTS | Uncommon Files |
| .COMMON | Uncommon Files |
| .COMMS | Uncommon Files |
| .COMPACT | Uncommon Files |
| .COMPANY | Uncommon Files |
| .COMPARE | Uncommon Files |
| .COMPARISON | Uncommon Files |
| .COMPAT | Uncommon Files |
| .COMPILERS | Uncommon Files |
| .COMPLICATI | Uncommon Files |
| .COMPOSER | Uncommon Files |
| .COMPPIANO | Uncommon Files |
| .COMPRESSIO | Uncommon Files |
| .COMPRESSOR | Uncommon Files |
| .CON | Web Files |
| .CONCERTO | Uncommon Files |
| .CONF | Settings Files |
| .CONFERENCE | Uncommon Files |
| .CONFIDENT2 | Uncommon Files |
| .CONFIDENTI | Uncommon Files |
| .CONFIG | Developer Files |
| .CONFIGDBLI | Uncommon Files |
| .CONFIGS | Uncommon Files |
| .CONFIGURE | Uncommon Files |
| .CONNECTION | Uncommon Files |
| .CONSEQUEN | Uncommon Files |
| .CONSOLE | Uncommon Files |
| .CONT | Uncommon Files |
| .CONTACT | Data Files |
| .CONTENTS | Uncommon Files |
| .CONTENTSON | Uncommon Files |
| .CONTROL | Uncommon Files |
| .CONTROLPAN | Uncommon Files |
| .CONV | Uncommon Files |
| .CONVERSION | Uncommon Files |
| .CONVERT | Uncommon Files |
| .CONVERT2 | Uncommon Files |
| .CONVERTER | Uncommon Files |
| .COO | Uncommon Files |
| .COOKIES | Uncommon Files |
| .COOL | Uncommon Files |
| .COP | Uncommon Files |
| .COPIER | Uncommon Files |
| .COPIEREC | Uncommon Files |
| .COPPER | Uncommon Files |
| .COPY | Audio Files |
| .COPYING | Uncommon Files |
| .COPYR | Uncommon Files |
| .COQ | Uncommon Files |
| .COR | Data Files |
| .CORE | Uncommon Files |
| .CORELPROJE | Uncommon Files |
| .CORELSHOW | Uncommon Files |
| .CORRECT | Uncommon Files |
| .CORRECTION | Uncommon Files |
| .CORTOUCHKA | Uncommon Files |
| .COS | Settings Files |
| .COS3 | Uncommon Files |
| .COSMO | Uncommon Files |
| .COSMO2 | Uncommon Files |
