If you want a single instance of "th" without superscript formatting, just Undo
(for example by pressing Ctrl+Z) immediately after Word has changed the format
of text.
This is excellent advice. I have lots of autoformatting options set
because I *usually* want them. Ctrl-Z allows me to selectively cancel
them so that I get the best of both worlds. It works for the ordinals
(1st, 2nd), lists (ordered and unordered), smart quotes, indents, etc.
It also works for autocorrect when Word is a little too helpful.
Set the autoformat and autocorrect the way you usually want them, then
use Ctrl-Z to override.