| chk | Saved File Fragment |
| chk | Epidata Defined Checks |
| chk | Gaussian Checkpoint File |
| chk | DB/TextWorks Check Textbase Problem Report |
| chls | Charles Session Data |
| chn | MODTRAN CHN Output File |
| chp | Affymetrix Probe Array Results File |
| chq | Help Combined Full-text Search |
| chr | Autodesk 3D Studio Max Character File |
| chs | MotionTracking Chromatic Shift Correction Data |
| cht | ZSNES Game Cheat |
| cht | ICQ Saved Chat Session |
| chv | ChView Interactive Star Map |
| chw | Compiled HTML Help Index |
| chx | AutoCAD Standards Check |
| chy | FileMaker Pro Data |
| ch_ | Compressed CHM File |
| ci | iBlaze Case Information File |
| ci | CitectSCADA Data |
| cia | Nintendo 3DS CTR Importable Archive |
| cib | Concordance Imagebase File |
| cid | EL-CID Data |
| cie | CIE Color Information Data |
| cif | ColorImpact File |
| cif | Crystallographic Information File |
| cih | Photron FASTCAM Camera Information Header |
| cii | Intergraph CAESAR II Data File |
| cik | CorelDRAW Graphics Custom Dual Tone Settings Data |
| cim | Cimplicity HMI Screen |
| cio | SWAT Master Watershed Data |
| cip | Ghost Keylogger Logfile |
| cir | Racelogic PerformanceBox Circuit Overlay |
| cir | Cadence PSpice Circuit Data |
| circ | Logisim Circuit Data |
| cis2 | CIMSteel Integration Standard 2 Document |