It is not mandatory to register the adoption deed.
HEADNOTE:In order that an adoption may be valid under the Hindu Law
there must be a formal ceremony of giving and taking.
“there cannot be a valid adoption unless the adoptive boy is transferred from one family to another and that can be done only by the ceremony of giving and taking. “
“"The giving and receiving are absolutely necessary to the validity of an adoption. They are the operative part of the ceremony, being that part of it which transfers the boy from one family into another. But the Hindu Law does not require that there shall be any particular form so far as giving and acceptance are concerned. For a valid adoption, all that the law requires is that the natural father shall be asked by the adoptive parent to give his son in adoption, and that the boy shall be handed over and taken for this purpose." “
Supreme Court of India
Lakshman Singh Kothari vs Smt. Rup Kanwar