Observations:
The initials G E D are obviously the end of the word discharged, presumably from the Polish forces. Does the document give no clues at all relating to previous service?
The original number is not a British Army number, perhaps Polish.
The PRC was a British Army unit. I assume that his record from that time would be held, with all other British Army records of the time, by the Ministry of Defence. Your friend may wish to consider applying for them with the name Kitzinger and the new number. The process is described here:
https://www.gov.uk/get-copy-military-service-records/apply-for-someone-elses-recordsHis name does not appear on the National Archives listings relating to POWs.
There is a naturalisation certificate record of 1954 in the name of Alojzy Antoni Piotr Kitzinger at the National Archives. If this is your man then presumably the family know this.
https://discovery.nationalarchives.gov.uk/results/r?_q=alojzy+kitzingerWhy change his name - unlikely to be anything to do with the army. Perhaps tied up with the complicated history of Poland in his life time.
This web site may be worth contacting?
http://www.kresyfamily.com/9-polish-armed-forces.htmlI see nothing else that can be squeezed out of this record from a military standpoint.
MaxD