Possible Bug with File Manipulation
I found one other issue when trying to delete a file with the UE4/DFP combo.
When trying to add the delete file server behavior, I only get a popup stating:
"There are no delete or update transactions on page. Please insert an appropriate transaction first."
But, there actually is a delete transaction on the page and it used to be in DFP 2 that the user could create the trigger based on any number of events for the delete file to happen.