The easiest way is not to try to “type” into Tera Term, just use its macro support. From your DataGridView click event, generate a .ttl file like: sendln "your command here" Then run it with: Process.Start("ttpmacro.exe", "myscript.ttl"); That’ll send the command straight into the right Tera Term session. If you don’t need Tera Term at all, just use SerialPort.WriteLine() in C# instead.

Just for nitpicking: Even if the system FontDialog doesn't show 'Terminal', the OP may very well be 'enabled to use this font', as he were asking. You can't force the system FontDialog box to show it, but you can write your own FontDialog, including all the alternatives that you would like to appear.