TDF - NicheInterests/mistfunk GitHub Wiki
TDF stands for TheDraw Font, several of which were bundled with the program. Each TDF file contains a little alphabet (numbers and punctuation also, if you're lucky) drawn in ANSI art or ASCII art, some coloured. Using them in TheDraw would allow you to type on your keyboard and have your input characters output on the screen drawn large in the selected font.
The bundled fonts weren't especially easy on the eyes -- better than nothing, perhaps, but only just -- and the secret of making TDF fonts was not widely understood, and the file format was only useable in TheDraw (today supported in IcyDraw and some figlet forks), which no underground artists were using after the introduction of ACiDDraw. Consequently the ANSI art mainstream (the underground artists) kind of forgot about TDFs and left them by the side of the road for Public Domain SysOps to enjoy, unaware that there was any better ANSI art out there and not socially connected with anyone who might draw them some.
This uneasy status quo eventually changed when Roy/SAC undertook a quiet campaign to take hundreds of excellent bespoke fonts made by underground ANSI artists and extend them into complete alphabets, saving and distributing them as TDFs. Now SysOps had the option of unknowingly plagiarising the typography of talented underground ANSI artists! We advise: you don't have their permission or consent to use their old letters in this way, please think again.