In case of former eastern provinces of the German Reich there was a lot of destruction especially of the Lutheran parish records. Some survived and are nowadays in central archives in Germany or Poland. The Catholic parish registers had a better chance to survive, some are also in central archives (mostly in Poland) or at the local parish office. Also a lot of other German files are nowadays in the Polish State's Archives.
In case of todays' German territory the situation is better: The parish records (Lutheran resp. Catholic) are either in central archives or at the local parish offices. Other files are located either in the State's Archives, in municipal or other local archives.
Some records had been filmed in the past decades and are available via LDS.
Without knowing details of your case it is difficult to give you an advice. Please contact me, if I can be of further assistance.