I need to know how can I go about getting my original birth certificate in a closed adoption.

I don't think it is possible for you to get a copy, it was a closed adoption, so no one, including you, are to know your birth mother. For travelling purposes you have an altered copy showing your adoptive parents, so getting a passport will be no problem for you.

Tick

You can't unless you find your original parents and they may still have a old copy.

Now there is a real copy in the courthouse, but they are not public.