| ck9 | Cook'n Cookbook Backup |
| cka | Comfort Keys Database |
| cki | Ansys Chemkin Kinetic Data |
| cki | Off by One Web Browser Cookie Data |
| ckl | DISA STIG Checklist |
| ckn | Disk Doctors CK Support Info File |
| ckp | PSI-BLAST Checkpoint Profile Data |
| cks | PSI-BLAST Checkpoint Sequence Data |
| ckt | Ansys Chemkin Thermodynamic Data |
| ckv | CheckVision Database |
| cky | DSOrganize Data |
| ckz | QuickSFV Checksum Database |
| cl | Carlson Survey Centerline File |
| cl | IconUtils Cursor Library |
| cl2 | Hy-Tek Meet Manager Results Data |
| cl7 | Free Clipboard Viewer Saved Data |
| clam | Adobe InDesign User Dictionary Data |
| classlist | SMART Notebook Class List |
| clb | Corel Mosaic 5.0 Library |
| clb | ICQ Contact List Data |
| clb | NoteTab Clipbook Library |
| clbu | Android Call Log Backup |
| clbx | MP3 Automagic CD Cover Creator Label |
| clc | Corel Mosaic 5.0 Catalogue |
| clct | RootCause Collect Data |
| cld | ClamAV Local Database |
| cldcvt | CD-LabelPrint Converted Data |
| cldlyr | Terragen Cloud Layer Data |
| cle | Icon Lock-iT XP Locked File Indicator |
| clean | Instagram for Android Cache Data |
| clf | ListPro Data |
| clf1 | Common Loudspeaker Format Type 1 File |
| clf2 | Common Loudspeaker Format Type 2 File |
| clh | NoteTab Clip Assistant List |
| cli | AquaCrop Climate Data |