We had a new bathroom installed with the idea that we would install the fixtures, there is a white cap over the toilet drain it looks permanent and we can't get it out can someone tell us how to deal with this?>

You have to cut it off with a hacksaw or Sawzall.

It is a test plug. It is glued to the pipe. Take hammer, and break it in the middle. Then, take channel locks and peel of the pieces. Milo

Joy nailed it! This is a test cap and will have to be cut out.
This white plastic membrane is there for two reasons,
1. To make the fitting water tight when we fill the stacks for inspection,
2. To keep dirt and debris from falling down the closet bend. Cut it out and you'll be just fine, Good, luck, Tom