Is there a way to create a macro that highlights data based on another data source and calculate the differences compared to the source data?

Your post is quite ambiguous. What data sources, what is to be highlighted and what constitutes a calculation of differences?

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]

I'm in a office pool and I want to compare my selections to everyone else's and calculate the total differences between my selections and theirs. My selections will always be highlighted and I want only the selections that are the same as mine to become highlighted, then calculate each to show the total differences on each selection compared to mine.

Selections of what? A selection is only something you can see on-screen, with a range selected in an open document. You can't use VBA to compare what's selected on your screen against what someone else has selected on theirs.
What is this calculation supposed to return? A word count, character count, or something else?

If you're trying to compare documents, you can use Word's built-in Document Compare tools, without the need for VBA.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]