I am interested in installing a vent in a bedroom door to increase air
flow and circulation when the door is closed.  Have been unable to
locate any good references in this regard.  I am looking for a product
that I could purchase and easily install, or instructions for how I
could do this work on the door myself.

A vent about 12 centimeters above the floor may make the room cooler
when central air conditioning and warmer when central heating.
Problems should be rare unless the vent dimentions exceed 31
centimeters = one foot. If you have a Home Depot near you, pick out
the cheapest vent you think will do the job and take it to the do it
you self advice counter. They will likely have some helpful
suggestions.   Neil