It's not hard to select text via VBA. It's also not difficult to place selected text into a footnote. You won't even have to copy and paste!
One of the questions you might have to ask is how much text do you want to select? A paragraph? A sentence?
Be aware that Word considers "Hello Dr. Honey, how are you?" as two sentences because of the period after "Dr":
"Hello Dr." and
"Honey, how are you?"
This script may not do exactly what you want, but hopefully it will give you ideas. The script selects a sentence and inserts it as a footnote.
Code:
Dim x As String
With Selection
.Collapse ' Start by collapsing current selection
.Extend ' Select the entire sentence
.Extend
.Extend
End With
Let x = Selection
Selection.Footnotes.Add Range:=Selection.Range, Text:=x