I m trying to open a 2013 SW file on SW 2012 but it gives me some error about future version . but I really need this file and i can t replace or create it again . what should i do?
You can't. But you could save it out as a parasolid / iges / step etc and import.
If you upgrade to 2012SP5 I think you can open it to view - not sure about to model though.