“The clerks in the elections office had to open them, read the ballots, and throw the Trump ballots in the trash.”
When I was in charge of elections we used the IBM punch cards — the kind with the “chads”. None of the absentee envelopes were opened until election night after the polls closed. They were opened quickly by a panel of equal number of Rs and Ds. Then they were batched together, and run through the machine along with the ballots that were coming in from the precincts.
The mail-ins envelopes shouldn’t be open until election day/night, in the presence of watchers.
We used the same procedure when I was an election judge. There were always watchers. There was also a "two-man rule" for every other aspect of ballot handling by the judges. The two judges had to be of different parties.
Obviously they are not following these procedures in PA.