TD files are configuration files for the DOS based Borland Turbo Debugger. This program largely became obsolete with the advent of Windows. It might still be possible to access a .TD file whilst running an early version of Turbo Debugger (version 1 recommended) on a Windows DOS emulator.
Alternatively the TD file is also associated with the Microsoft rail simulation package Train Simulator, and, as such, it should be opened with this software.