Access does not have an automatic footnoting utility as does Word. You will
need to proceed manually or with custom code. If you have Access 2003 or
earlier, and if the question is about having a superscript character, you
will probably need to have the number in its own text box, formatted as
needed.
Stephen Lebans has on his fine web site a method for using a variety of
formats within a single text box. I have not used the system, and do not
know if it would answer your specific needs, but others have spoken well of
it. Here is the link:
http://www.lebans.com/richtext.htm
As I understand it, Access 2007 allows for mixed formats within a text box,
but I cannot offer any information about that.
If you mean something other than what I have guessed you will need to be
more specific.