Answer
The forward-looking approach is to read the document's content directly from EDM/File Storage and attach that to the email, rather than staging it through a server-side file copy first. An older, less durable pattern (copying the document out to a folder on the application server via a file-transfer utility API and pointing attach_ at that path) still works but depends on server-side folder access that isn't guaranteed to remain available as deployment architecture evolves; fetching the file content straight from Document Management's own storage for the attachment is the more current, portable technique.