List View for Closed Won Opportunities with no Documents

Problem

You want to create a list view to show all of the Closed Won Opportunities that do not have a Document attached. That way you can address Opportunities as needed. 

Solution

You would create a count rollup in order to count the attachments, then create a list view of Closed Won Opps with no attachments.

1. Create a custom Number field on the Opportunity object; this field can be hidden from the page layout if you'd like.
2. Create a new rollup in Rollup Helper
   1. Parent Object is Opportunity
   2. Choose the new custom Number field on the Opportunity object
   3. Child Object is "ContentDocumentLink" and "Related Object ID" as the relationship field. 
   4. Type of rollup is Count.
   5. Apply any filter criteria if you only want certain types of documents counted, then Save and Run the Rollup.
      
3. Create a list view which shows Closed Won Opportunities, where the Rollup count is 0, to take care of the issues.