Will paper invoices disappear for foreign customers once KSeF is introduced?

That depends on the agreement with the business partner. KSeF applies only to transactions within Poland. For foreign clients, the invoice must still be delivered outside the system – e.g. as a PDF, EDI, or other electronic format, and if necessary also in paper form. In practice, paper invoices may gradually disappear if both parties accept an electronic format. However, where the partner requires traditional documents, paper will still be in use. Foreign entities with a permanent establishment in Poland will be required to use KSeF.