How do I test the finish of a painted wood door?

Question

When painting over a wood door, I am not sure what the finish is whether it is oil or latex paint. What can I use to check a area of the paint so I will know what type of paint to use.

Answer 1

Put some acetone-based nail polish remover on a cotton swab.  If the paint comes off, it's latex, otherwise it's oil.

Answer 2

if you put primer on the door first you can put either oil or water based  paint with no problems