You cannot interrogate "explorer" as that process is already running before Pega Robotics can interact with it. In addition, the Path property is simply the path to the executable. The Arguments property is where you'd place any arguments (what you pass after the exe).
I will work with Excel files. But I found out, that there are Connectors in the Toolbox for Excel. I have only made the "Pega Robotic Automation Architect Essentials" Training, so it´s a Little bit difficult to know how it works. Can you suggest me a Training?