The following is the definition of information under Sec.2 f
(f) “information” means any material in any form, including records, documents, memos, e-mails, opinions, advices, press releases, circulars, orders, logbooks, contracts, reports, papers, samples, models, data material held in any electronic form and information relating to any private body which can be accessed by a public authority under any other law for the time being in force;
There is no such "classified document" with public authorities other than exempted organizations.
The burden of proof that it is exempted under Sec. 8 (1) of the RTI Act rests on the Public Information Officer.
You can add another point "if the information is exempted", please provide a certified copy of such directive/circular/order from the competent authority under RTI Act.