If you are looking for info regarding your adoption or about another person, you may be in for a long hard search. "Closed" means that. You would have to find a judge willing to hear the case, and get an appeals court order to reopen. You will need a lawyer and you will need very good reason to try and reopen.

https://www.askmehelpdesk.com/adoption/looking-birthparents-children-given-adoption-401680.html

That sticky is at the top of the adoption pages. It is the best advice I have for finding a child placed for adoption, especially in the closed adoption years.

Please remember that your child may have NO IDEA that he is adopted. Searching for him and finding him may completely uproot and possibly destroy his life if he has no idea. Be careful as you search, and think two or three or ten times about the entire situation before making contact.