LoTW uses four kinds of files, distinguished by Filename Extension.
| Filename Extension | Icon | File Type | Created By | Usage |
| .tq5 | Callsign Certificate Request | TQSL | Callsign Certificate Request File submitted to ARRL | |
| .tq6 | Callsign Certificate | ARRL | Callsign Certificate File referenced and managed by TQSL (cannot be backed-up, recovered, or moved to another PC) | |
| .tq8 | Digitally Signed Log | TQSL or logging application | Digitally Signed Log File submitted to LoTW | |
| .p12 | Personal Information Exchange | TQSL | Certificate Container File managed by TQSL; can be backed-up, recovered, or moved to another PC | |
| .tbk | TQSL Backup | TQSL | Backup File created by TQSL that contains all certificates, station locations, and preferences in a form that can be backed-up, recovered, or moved to another PC |