There was a rootschat discussion on 10-11 January 2023 re a 1933 Scottish birth ref. containing 'AR' with the RD name given as 'NRH'
A response by Forfarian was as follows:
NRH in that context means that the child was adopted, and AR does indeed mean Adoption Register.
The adoption certificate can be viewed in a Scotland's People Centre, but it will tell you only the child's date and country of birth and the names of the adoptive parents.
You will not be allowed to see the child's original birth certificate. Only the adopted person or someone acting on behalf and with the express written authority of the adopted person is allowed to see the original birth certificate.
Unless, that is, you already happen to know the child's birth name, in which case you can see the birth certificate in the normal way. As it's 1933 you would have to order it to be sent to you.
I have not used it, but I understand that the adoption register comes in the form of a microfiche.