File, Open.

But if you open a Pro file with Premium, it cannot be opened again in Pro.  If you ever do bookkeeping for more clients, you might want to consider becoming part of the Partner program.  You will then get a copy of the Accountant's Edition that will allow you to open Pro, Premium or Quantum of the same version year and release.

If you need to keep it in Pro format, your best option is to use one of the Remote control software options available these days.

Oh, I didn't imagine it would be that easy! Thanks!