I have been having some unusual things happening with Word and cannot figure
out how to make them not happen!  An example:

When I make a “selection” in order to make changes, such as bolding,
changing fonts, etc., then institute the change, the whole document changes
instead of just the selected section.  I can “undo” each time and the change
remains, but it’s a nuisance, especially if the document is long, contains
graphics, etc., because then it is slow to recover to the original.  It will
even change separate text inside text boxes.  I’ve checked and unchecked
every option I can think of to see if it makes a difference.