Is judgement in a criminal case, a public document

The judiciary does not come under the purview of RTI Act. Every judgement is not for the public nor it is public document. If you are  not party to the case then you are not entitled to obtain the certified copy of the order.

Section 7 (9) says thus

7 (9) Any information shall ordinarily be provided in the form in which it is sought unless it would disproportionately divert the resources of the public authority or would be detrimental to the safety or preservation of the record in question.

You have to elaborate on what you asked to find out on what exact grounds they rejected. It will not be difficult to get over this problem. All judgments are public documents. Plain refusals can only be under Section 8.