RdrCEF.exe dont close

Hello 

I have Windows Server 2016, users connect with RDP to Server.

If user opend PDF or FDF file, and after close Adobe Reader the process RdrCEF.exe still running in TaskManager. Why dont close this executable file?

When user Log Off in RDP, Windows must close this proces, and write on screen :   GDI + Program immediatly close, Windows close it, and succesfully Log Off.
Please FIX, if close user PDF immediatly close this process. Thank.