in DLP settings, you can configure "scan within attachments".
So... this means that the CCL lists and the admin-defined keywords are beeing considered not only in the subject and the plant-text body of the mail, but also within the attachments. Fine.
So the question is: can you provide a list of (currently) supported attachment/document types?
I tested with Windows (.docx) and it works, but it´s not easy to find out by try-and-error...