I don't mean "strikethrough". I mean to have a character typed on top of
another character so that they are combined into one. In MS word it's
referred to as overstriking.

It's not covered in MOS, it's not in Word Help, Googling suggests it can't
be done per se. Where did you hear it referred to as overstriking in Word?

Perhaps you're trying to combine 2 characters so the result looks like
something else. In a blank sheet,

=CHAR(ROW())

in A1 & copied down to A255 will show some special characters you can
access. Forex, use ALT+0216 for the character the above gets you in A216
(NB - type "0216" on the number keypad).

If this doesn't cover it, post more details.

Rgds,
Andy