Assuming you will send a mail notification, you will need the email module.
Then you have two options
1) Run a scheduled event at a certain interval that sends out the reminders
2) Use an After commit event on the uploaded documents entity to send an email
I just tested this one: https://appstore.home.mendix.com/link/app/112194/ it will update the icon when new notifications are created. Works like a charme.