Confusingly, B&R had 2003, 2005, and 2010 products and those number do not have anything to do with the year they were introduced (they are all considerably older). I don't think Profibus would let you communicate to the PLC, there should be a serial or Ethernet port for that, but I could be wrong (I never used any of the 3, they were old news when I started nearly 15 years ago).
If you have Automation Studio, but no source code, you should still be able to see hardware status and even variable status for compiled routines on the PLC, just not the code itself. You'd be looking at AS2.7 as the newest version that would work and maybe older. If it was programmed PG2000, then I wouldn't even bother trying to connect. You'd have to get your hands on PG2000 and run it in a dos box and try to get it to see your serial port to communicate... easier to get a computer from a museum up and running than to get a modern computer to work with it.