You're script will need to use Export Field Contents to export the file before your send mail step can attach it. You can compute a file path and name for the file. Store it in a variable. Export the field using this variable. And then your send mail script can refer to this same variable to attach it to the email that you are sending.
(And if the container file is always inserted with the store by reference option, you can extract the file path from the container to avoid the export field contents part of this operation.
Thanks PhilModJunk, that worked exactly the way I wanted!