Not sure all what DFP can do, but you need to end up with the filename in a database field, and the files uploaded to a designated folder. I used a different extension at one point that uploaded the file and did the insert as well.
Once that's taken care of, in UE, attachments tab, you can select a dynamic value from the recordset by clicking the little icon next to the text field. It will insert some script, then ahead of that manually enter the path to the file.
statements/< php or asp script >
(statements in this example is the folder the files end up in)
I would do lots of testing to make sure people don't end up with the wrong statements!