Perhaps this is more of a question to the person who has sold you the PROFIBUS DP converter. It really can be converting it to anything both hardware and software wise. Perhaps the easiest option is Modbus, which everyone apart from Siemens accepts as a common industrial standard.
Be careful if using the inbuilt RS232 port on the R1 controller. It does not have a very big communications buffer and if you get some strange voltage pickup on the cabling, you can end up blowing up your SNAP-PAC-R1 controller. Rack mounted SNAP comms modules provide optical Isolation and dedicated processors for communications handling.
BTW. You could save on the external converter and an RS232 / 422/ 485 SNAP communications module by directly buying a SNAP-SCM-PROFI module for your R1 rack. Heres a link to the relevant datasheet SNAP-SCM-PROFI Communication Module
Although as usual with everything Profibus, you either have to be German or a bit of a Siemens guru to get it working. Here is a link to the Opto22 technical documentation for starters. OPTO22 PROFIBUS-DP Master Software