What documents in original shall be provided in the quarterly CBAM report?

No document in original needs to be provided. The reporting declarant must only submit the required information for the quarterly CBAM report through the CBAM Transitional Registry.

According to the principle of transparency outlined in Annex III section A.2 of the Implementing Regulation, complete and transparent records shall be kept at the installation of all data relevant for determining embedded emissions of the goods produced, including necessary supporting documents, for at least 4 years after the reporting period. Those records may be disclosed to the reporting declarant. Such records may be requested by EU Member States in case of a review of the quarterly CBAM report.

Source: EC’s Questions and Answers on CBAM 

CBAM Regulation