Thanks, your edit is perfect:

		$attachment[] = array(
		 'att_file' => $pathtofile,
		 'att_mime' => 'application/pdf',
		);
		//Add attachment to Frontend PM post
       FEP_Attachments::init()->insert( $message_id, $attachment );

I can clearly see that your modification the the database is much better. Now on to OpenEMR. I will look at FEP_Message_Query. Thanks again,
Craig