In ProSeries, Manage Users for employees has two settings... Admin and Employee. The only difference between these settings is that the Admin can invite or remove users for the ProSeries program. Otherwise they behave the same while in the ProSeries program.

This means an employee can delete client files by design.

If you want to restrict what different users can do in the ProSeries program, you'll want to enable Access Rights (under Tools / Users & Access Rights) to assign Roles which control user access.