DHL Paket International shipments to Switzerland now support Paperless Customs. You no longer have to print the customs invoice and attach it to the parcel, because the invoice from your order is sent to DHL electronically when you create the label. 

Activate Paperless Customs in the Setup » Orders » Shipping » Shipping service provider » DHL shipping » Shipping settings » [Open shipping combination] under International shipments (visible when export delivery is activated).  It is deactivated by default.