You need WinCC Flexible Advanced 2008 SP2 to convert the Protool Pro projects.
Not sure if you can even purchase the Powerpack to upgrade from Standard to Advanced, and then get 2008 SP2. You will probably get 2008 SP3, and then you are stuck again.
I think you need to consider what you want to do in the long run.
Even if you managed to convert the panels to WinCC Flexible 2008 SP2, then you will find out that all the panels that are supported by WinCC Flexible have been discontinued. That are all the TPx77, OPx77 and MPx77 panels. You can still purchase them as spares, but the prices are steep and will become more steep over time.
So I am thinking that you should consider to get WinCC Advanced v13+Sp1.
With that you can migrate to the latest panels (which are both much better and much cheaper), and be able to maintain the programs in the long run.
And the Protool Pro PC Runtimes should be migrated to WinCC Advanced PC Runtimes.
So you still need someone to do the conversion from Protool Pro to WinCC Advanced PC Runtime.