I know, you always see these shows on TV about a tearful reunion of mother and daughter and how they have both been looking for each other for years. Sure, that happens but sometimes, the biological parent don't want any part of their child, often their parents are long dead. There are many reasons why kids are put up for adoption so if you look for your biological parents, don't get your hopes too high. After all, they had to have a reason not to raise you themselves.
As legal adults, most people have the rights to access original legal documentation and so discover and trace their genetic and biological history... But this right varies state by state for adult adoptees. Parents and guardians of underage children have the right and responsibility to make choices for their children and to protect them from influences and knowledge that they feel might cause harm to them. But when that child becomes an adult, he or she should be able to request and receive the legal, original, documentation of his or her birth since he or she is now old enough to effectively make their own choices and deal with the consequences of them for good or bad.
Attempts to prevent this are unconstitutional and it places the rights of some adults over the God given right of another adult to self-knowledge and knowing their biological roots/family/extended family.
A parent can make a choice for a child, but that same parent cannot make a choice for an adult.