If PaperStream Capture is entirely frozen and you are unable to scan or exit the application, a force close using Task Manager would be the best route to take without having to restart your PC.
NOTE: This will close the program and any scans that was being scanned the moment it froze will need to be scanned again.
To launch the Task Manager, please click on the Start Menu of your windows computer (bottom right windows icon) and type in Task Manager. Then select Task Manager from the most top option.
The Task Manager will launch. Please locate the PaperStream Capture > Select it so it gets highlighted > Then press End Task to force close the application.
This will allow you to launch PaperStream Capture once more and scan normally again.