If your customers are not receiving any files that you attach when you create a new ticket on their behalf, you'll just have to enable this setting in your New Ticket Auto-responder email notification.
Step 1: Head on over to Manage >> Notifications >> Contact Notifications, and click on New Ticket Auto-responder.
Step 2: Scroll down to Templates, and click edit next to the template you're using.
Step 3: Enable the check box next to "Include attachments" under Template options and hit Save Settings.
With this in place, your customers will now receive any files you attach when creating a ticket on their behalf.