You might try other techniques for selecting text rather than trying to rely
on the dragging method. For example, try just clicking at one end of the
passage, scroll (using the scroll bar) until you can see the other end of
the passage, then hold the Shift key while you click at that spot. You can
also:
Triple click a paragraph, then Shift+Click another,
Control+Click a sentence, then Shift+Click another,
Double-Click a word, then Shift+Click another,
as well as using the left margin (selection area): Click to select a line,
then Shift+Click another.
There are any number of additional selection techniques which are far more
efficient & effective than dragging. See Word Help on: Select text and
graphics.