Q: Preview app is not working all menu buttons are grey

Hello !

            Kwindla

If any problems occurs in preview some terminal  commands are in the article , please follow them step by step .

  Resolve issues caused by changing the permissions of items in your home folder - Apple Support

Also to run sudo command first create root user account , after executing the command log out from root user account.

Suggested article how to create root user account : Enabling and using the "root" user in OS X - Apple Support

Thanks !