Yes, you can file RTI for a copy of your exam paper from Himachal Pradesh State Open School. The HPSOS has been established under the auspices of the H.P.Board of School Education Dharamshala-176213 on the basis of a Project Proposal designed and developed in collaboration with the National Institute of Open Schooling(NIOS),Ministry of Human Resource Department,Govt.of India.The Secondary Education Programme through SOS is functional from the academic session 2011-2012 and Middle and Senior Secondary Courses are functional from 2012-2013.
Hence, it is a Public Authority under section 2(h) and is liable to provide information under section 2 (f) and 6(1) of the RTI Act, 2005.
As per the Hon'ble Supreme Court by judgment in Central Board of Secondary Education (CBSE) Vs Aditya Bandopadhyay (2011) 11 SCR 1028, declared that all the exams, conducting bodies are bound to disclose answer sheets to the students or candidate.
The RTI application can be made to the designated PIO along with payment of fees and copy of admit attached along with application.
To file application for copy of exam paper please refer https://onlinerti.com/how-to-file-rti-online-for-exam