how to require users to add file to objects

We have an Object type setup called Customer Requests that can have files.  What is the best way, assuming it is possible, to require our end users to add a file to this request, either at time of creation or within workflow?  All of these requests we get from our customers via email and are entered into M-Files by internal staff.  We want to make sure that form provided by the customer is added to the request in M-Files by our internal staff.