| tfd | Tape Format Requirements Document |
| tfrd | Tape Format Requirements Document |
| tft | Text Formatter Plus Formatting Data |
| tg | TuxGuitar Document |
| tgf | Trivial Graph Format |
| thing | MakerBot Thing Document |
| thl | Total 3D Home Design |
| thml | Theological Markup Language Document |
| thmx | Microsoft Office 2007 Theme |
| tii | TI Interactive Workbook |
| tkl | Takeoff Live Document |
| tlg | Intuit QuickBooks Transaction Log |
| tlq | Art Explosion T-Shirt Factory Deluxe Document |
| tm | TeXmacs Document |
| tm3 | TreeMap Document |
| tm5 | Adobe Pagemaker 5.0 Template |
| tm6 | Adobe Pagemaker 6.0 Template |
| tmbak | TextMaker Document Backup |
| tmd | TextMaker Document |
| tmdx | TextMaker 2018 Document |
| tmv | TextMaker Document Template |
| tmvt | LexisNexis TimeMap Template |
| tmvx | TextMaker 2018 Template |
| tns | TI-Nspire Document |
| tnsp | TI-Nspire PublishView Document |
| tnv | Bitware Fax Document |
| toc | Adobe FrameMaker TOC |
| top | Topocad Drawing Document |
| top | Adesso Cyberpad Handwriting Document |
| topviw | TopSolid Viewer Document |
