When using ndOffice versions 1.8 and newer, the notifications use the built-in Windows notifications (in Windows 7 these are bubbles; in Windows 10 these are rectangular banners).
In Windows 10, these notifications are managed in the Windows settings menu found here: Settings > System > Notifications & actions > ndOffice
Notifications - turns all ndOffice notifications ON or OFF
Show notification banners - turns banners in the system tray ON or OFF
Keep notifications private on lock screen - when the screen is locked, notifications can be made private
Show in action center - turns notifications in Action Center ON or OFF
Play a sound when a notification arrives - sound can be turned ON or OFF