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 |