Yes, you can file RTI application for getting the Certified copy of the Marriage Certificate. The sub registrar offices come under the Revenue department of the states and hence, are Public Authority under section 2 (h) and are liable to provide information under section 2 (f) and 6 (1) of the RTI Act, 2005.One of the functions of Sub Registrar is to Solemnization & Registration of marriages and maintain the relevant documents of the same. The application should be made to the concerned Sub registrar office where the marriage was registered. In the application you must mention the date of registration, name of the parties and address. The requite fees must be paid along with the application.
For further assistance to file application for copy of marriage certificate please refer https://onlinerti.com/