Why would they need a button, when triple-clicking would select the whole paragraph?

You also need to be aware that VBA has no idea what a grammatical sentence is. For example, consider the following:
Mr. Smith spent $1,234.56 at Dr. John's Grocery Store, to buy: 10.25kg of potatoes; 10kg of avocados; and 15.1kg of Mrs. Green's Mt. Pleasant macadamia nuts.
For you and me, that would count as one sentence; for VBA it counts as 5 sentences.

A button-based solution would require VBA.

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