Which documents should I attach to the parcel?
Attach an address card with the sender and recipient address details for domestic shipments (within the Baltic countries) and for international shipments add custom declaration if needed.
The customs declaration form can be found on the address card or as a separate form, available for printing in multiple copies. Remember that all copies must be printed out and added to the shipment.
You can read more about address cards here: How to create, print, and attach an address card.