I can write a regular expression to pull out the footnote text from the above string. And I can write another regexp to insert that text in the appropriate place in the main body. But I don't know Perl.

Then this is the perfect occasion for learning Perl. Start with perlintro.

If you need any specific advice because you don't understand something from that tutorial, feel free to ask.

But we are not a code writing service, so you'll have to show some effort on your own.