Whats the number of times the letter d appears in:
Q: Notification to document owner when file is going to expire (SharePoint Online) Could someone advise me how to set up a notification workflow that will send an email to the document owner 

A: Check out Information Management Policies.
You can create a suitable policy that will trigger an alert or an workflow when a certain condition is met. 
You can read about it here: https://support.office.com/en-us/article/create-and-apply-information-management-policies-eb501fe9-2ef6-4150-945a-65a6451ee9e9
The other option is simply to create a workflow which pauses until its time to send the notification email. This is a quick and dirty solution and comes with some caveats:


*

*The workflow will be running until the pause until condition is met. This means that any updates on the list item, such as an update to the field used for expiration, wont update the workflow.

*Since the workflow is running any updates to the workflow wont really matter until either the workflow is stopped or finished.


To be frank: This is in 99% of the cases not feasible. The proper way to do it is to use a policy which starts a notification workflow when the proper condition is met.
Cheers

A: There are at least two options to achieve this.
Use Information Management Policy, define retention stages. Under List Setting -> Information Management Policy Setting -> Enable Retention and Add Retention Stage. You can start a workflow based on the retention. 

Create Calculated Column with formula e.g. =[Contract Expiry Date] - 2, and create a workflow to send an email based on the status/calculated column.
Similar issue post for your reference:
Notifications for expiring documents in SharePoint Online (2016)?

user
The passage contains 36 "d"s.
assistant