Complex sentence: Later he was accepted and attended the Escola Politécnica do Rio de Janeiro (today's Escola de Engenharia da UFRJ); at which time he worked as an intern the Firma L. Riedlinger (an engineering firm located in Rio de Janeiro).
Split into simpler sentences: Later he was accepted and attended the Escola Politécnica do Rio de Janeiro (today's Escola de Engenharia da UFRJ). While attending the Escola Politécnica, Baumgart worked as an intern with the Firma L. Riedlinger (an engineering firm located in Rio de Janeiro).