There is no reason to think that Platte River Networks knew that there was secret stuff on the Clinton server. After all, it would be illegal for Clinton to have secret stuff on that server.
I doubt that they have any liability, criminal wise. They simply didn’t know that the Clintons run a criminal network.
Another story today says this same company is accused of created software to help congress critters avoid leaving a trace or track of their communications.
Maybe that is why Clinton picked them. If that was what they were doing, no doubt Hillary knew about them.
At least there is one thing we haven’t heard in all of this mess -
It’s Bush’s Fault. :^)