Use Case: 
I would like to generate mutliple documents at once and using Process Builder to trigger the flow but something is not working. What am I doing wrong?

Development Team Reply: 
Mass generation of documents will not work with Process Builder because of Salesforce and Google Drive limitations. If you wish to generate multiple Documents at once, using list views for example, you need to enable Batch Mode. However, you also need to modify Process Builder flow that you are using to start generation of documents:
-Instead of using Apex type of action, you will need to use ‘Create Record’ type of action where you will be creating new Document Request records.
-NOTE (which may change later): Mass generation of documents does not currently work for Developer edition Salesforce orgs so our batch feature not yet available in this type of org.