Hi blue_line,
NAC is 'Non Availability Certificate' which is issued by the municipal councils in India if they cannnot locate your birth record. It just says that :
A search was made for the birth records of <your name> on the request of <father's name> and the same were not found.
IF you do not have a birth certificate and it can not be issued, you have to get this NAC and sworn affidavits of two persons who were adults at the time of your birth that they know you since your birth. something like this:
I <name> hereby declare under the perjury of law that I know <your name>
since birth because I am his/her mother's brother(or any other relation).
I was present at the time <your name> was born to <your father's name> and <your mother's name>.......
Get this from two persons. May be your uncle or aunts or father......
The format of the BC depends upon the MC issuing it, but make sure it is in English otherwise you have to get it translated....
Hope this helps