I suggest to use the assembly comes with the package. Any other assembly may not be fully compatible with our payment.
In the case you find out the assembly is no longer working due to breaking changes from Paypal, please notify us by filing a bug report.
Thanks for getting back. I don't feel particulally happy about adding random DLL's in my solution especially when it comes to something important as taking users payments. I understand that Episerver has build the code to work with this DLL and new versions will not work but where did EpiServer get this DLL from? if it came from PayPal, I assume that we can get it as part of a NUGET package or something.