Section 5 of the Hindu Adoptions and Maintenance Act, 1956 applies to:

Section 5(1) says no adoption shall be made after the commencement of the Act "by or to a Hindu" except under its Chapter II, and section 10(i) requires the child adopted to be a Hindu. So the Chapter governs Hindus adopting Hindus after the Act came into force, not all residents of India and not adoptions made before 1956.