Just save the license file to a folder on your hard drive (doesn't matter where).
Then start Plant Simulation and choose the menu item Tools->Preferences.
In the now open preferences dialog go to the page 'License'.
Select the checkbox in front of the license file edit box and press the button on the right side to open a file select box where you can choose your license file.
You also have to change the license type to 'Student'.
Close the dialog with 'OK' and everything should be fine.
One more remark: Since you have the folder C:\Programme you might have a German user interface.
Here you have to select the menu 'Extras->Voreinstellungen'.