| btkey | uTorrent License Key |
| btoa | Binary-to-ASCII Encoded File |
| btwsendto | Windows Bluetooth Transfer Options Data |
| buf | Buffer |
| buj | Personal Backup Saved Task |
| bup | DVD Information Backup |
| bvd | Bitdefender Vault File |
| bzi | DBAN Kernel Image |
| bzplug | Corel AfterShot Pro Plugin Bundle |
| c2a | Casio ClassPad II Add-in |
| c2u | Texas Instruments CBL 2 OS File |
| c32 | Syslinux COM32 Module |
| cache | General Cache File |
| calb | Coolect Album |
| cat | Microsoft Windows Security Catalog |
| cb | Microsoft Windows 95 Clean Boot File |
| cbds | Comic Book DS |
| cbs | Comodo Backup Job Script |
| cef | CenturionMail Encrypted Email |
| cgz | Linux Drivers Archive |
| chml | Chameleon Encrypted Database |
| chunk001 | File Splitter Split Archive Part 1 |
| cks | Windows CE ROM Image Checksum |
| cl | Cursor Library |
| clb | COM+ Catalog |
| clkw | Clicker Word Bank |
| clp | Windows Clipboard File |
| cn_ | Compressed Windows Help Content |
| con | OASIS Montaj Control File |
| contour | Contour Screenplay |
