I am a new home owner with an older furnace. I have a green pan mounted to a duct near my furnace, and a humidostat. I was told that was a humidifier. I have searched the net to try to educate myself on these. It seems there are missing parts to mine. I would like to remove the pan from the duct that it is attached to. It has rusted parts on it and I am affaid of what could be inside of that pan. Can I remove it and how would I patch hole( if there will be one) in the duct? Or should I even need to worry about it being there anyway.

Turn off the water supply and let it alone. Eventually if your furnace is that old it will need to be replaced and then you can have the contractor toss it out for you.