If you are using presenter view or another extended desktop option, the
presentation can remain on the current slide while you browse for things on
the local monitor.
If using a mirrored output (same thing on local monitor and projector) you
are limited in options. The best would be to see if the projector being used
has a "black out" option. Or you could change the input source on the
projector (where it will usually go to a blue screen or possibly to sleep).
