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 - turn on or off the ndOffice notification messages.
Show notification banners – show or hide notification messages in the notification area.
Keep notifications private on lock screen - show or hide notification messages when the screen is locked.
Show in action center - turn on or off the notification messages in the Action Center.
Play a sound when a notification arrives - turn on or off the notification message sound.