Tony Deb wrote:
What is the best way to paint an existing popcorn ceiling?

snip

Get rid of it. The easiest way is to duct tape a 8" drywall knife to
your shop vac hose/toolholder and scrape away. To mitigate concerns
about possible asbestos fibers getting loose, a little pre-misting with
a spray bottle will take care of it. Double bag the debris for safety.
Odds are your popcorn was mostly styrofoam based anyway as anything
else is a bear to apply. Good luck.

Joe