Pratham, you haven't mentioned regarding which examination purpose are you enquiring about the OBC-NCL certificate. This is important because few examinations have set a deadline for the OBC NCL certificates renewal. But in general, the validity of an OBC NCL certificate is 1 year. And so if you got your OBC-NCL certificate this year in April, it is valid until next year March i.e. March 31st, 2021. So you can submit it during the admission process of the entrance examination that you are appearing for. This shall not be a problem.

Yes, you can. Well in fact most of us apply for these kinds of certificates when we need them for submitting in councelling, colleges, scholarship etc. So I don't think there is any problem if your certificate is authentic.