There are some things you could do to slow down people who have no idea of
how Word works. For example, you can intercept the copy and paste commands
with macros that don't do anything, or that pop up a nasty message. You can
unassign the shortcut keys.

However, it would take the average geek about 5 minutes to figure out what
you've done and undo it, and half that time for the average teenager.
Besides that, there are lots of other ways of copying things besides just
copy/paste (think Insert > File or an IncludeText field).

The honest rule of thumb is that if someone can see your document, and they
have an incentive to make a copy, they can. It's only a question of how much
effort it takes and whether it's worth it.

By the way, the "protection" of an Adobe PDF file isn't all that secure,
either.