I sent plain copies of our tenancy agreement, bank statements, and bills with my application. It was OK and the application was accepted.
However, when at the later stage I was asked for an update of the evidence that we live together, it was emphasized that I need to provide originals. We don't have "current tenancy agreement" as we are on a rolling lease after our fixed-term expired. And Poweshop doesn't provide any bills apart from sending pdf. My CO said that she knows abput Powershop and would be OK with printouts and she accepted a leter from our property manager stating that we both have been living at the same property for more that 2 years.
So my guess would be that sending printouts would be OK unless you are asked for certified copies or originals.