| ize | IZArc Encrypted Archive |
| j01 | Akeeba Multi-part Backup Archive |
| j01 | Akeeba Secured Backup Archive |
| j02 | Akeeba Multi-part Backup Archive |
| j02 | Akeeba Secured Backup Archive |
| j03 | Akeeba Multi-part Backup Archive |
| j03 | Akeeba Secured Backup Archive |
| j04 | Akeeba Multi-part Backup Archive |
| j04 | Akeeba Secured Backup Archive |
| j05 | Akeeba Multi-part Backup Archive |
| j05 | Akeeba Secured Backup Archive |
| jar | Java Archive |
| jbackup | The Journal Backup Archive |
| jdb | Symantec Endpoint Protection Update |
| jgz | JNode Module Package |
| jisp | Tkabber Emoticon Set |
| jma | NSRT Compressed Game ROM |
| jpa | Akeeba Multi-part Backup Archive |
| jpa | JoomlaPack Backup Archive |
| jps | Akeeba Secured Backup Archive |
| jp_ | Compressed Microsoft JPEG Image |
| jrc | JRchive Data |
| jsonlz4 | Mozilla Firefox Compressed Bookmarks Backup |
| jva | Junos Firefly VM Package |
| jzip | JZip Archive |
| kb2 | Kleo Backup Archive |
| kde | Kaspersky KryptoStorage Container |
| kdz | LG Smartphone Firmware Update |
| keb | Kaspersky Anti-virus Virus Bases Data |
| kgb | KGB Compressed Archive |
| kge | KGB Archiver Encrypted |
| knar | KNIME Workflow Archive |
| kodi | Kodi Update Data |
| kry | Krypter Encrypted Data |
| ksp | KeyShot Package |
