The two most important documents in the process of transfering credits from abroad are the Online Learning Agreement (OLA) and the Transcript of Records. Keep in mind that your faculty/department/institute is responsible for the accreditation of academic achievements from abroad, not the International Office.
The credit transfer is based on the European credit transfer and accumulation system (ECTS), the examination regulations (Prüfungsordnung) of your individual study programme at Ruhr-Universität Bochum (RUB) and the Lisbon convention (page only available in German).