Complex sentence: The father of Otto F. Walter died in 1944, and he graduated, after first working in the father's company, a volunteer at a printing company in Köln, he worked for the publisher Jakob Hegner as editor, before returning to the Walter Verlag.
Split into simpler sentences: The father of Otto F. Walter died in 1944, and he first worked in the father's company. But soon he volunteered at a printing company in Köln, and he worked for the publisher Jakob Hegner as editor, before returning to the Walter Verlag.