| cql | XDCC Catcher Queue List |
| cqs | ConQuest Saved Search File |
| cqt | Mail.dat Container Quantity Data |
| cr0 | Autodesk Moldflow Cool Analysis Restart File |
| cr2 | Poser Character |
| cr3 | Casio WK-1800 Registration Data |
| cr4 | STABCAL Calculation Data |
| cram | CRAM Data |
| crashed | AbiWord Crash-Saved Document |
| crate | Serato DJ Crate Data |
| crc32 | CRC32 Checksum |
| crd | CARE-S InfoWorks Catchment Runoff Data |
| crd | Carlson 2016 Coordinate Data |
| crd | CHARTrunner Dashboard |
| crdb | Carlson 2016 Coordinate Database |
| crds | Windows CardSpace Backup |
| creole | Creole Source Code |
| crf | MOUSE Runoff Data |
| crg | OpenCRG Data File |
| cri | PLS-CADD Criteria |
| crl | Certificate Revocation List |
| crld | Clicker Crick Resource Library Data |
| crm | WRAP Conditional Reliability Modeling Data |
| crmlog | Microsoft Windows COM+ CRM Log |
| cro | AquaCrop Crop Data |
| cro | CropWat Data |
| crossdb | MixVibes Cross DJ Collection Data |
| crpd | Microsoft Windows SignTool Data |
| crpt | Cryptosaurus Encrypted File |
| crq | Blackboard Course Requests |
| crr | Cgatools CRR File |
| crr | SVAL Correction Data |
| crs | CompuTrainer Chart Screen |
| crs | Document Conversion Resource |
| crs3 | OmniPage Lite Data |