There are various relevant archival holdings in which you can search.
The first is the Europeana portal. Here you can discover tens of thousands of works of art, artefacts, books, videos and audios from all over Europe.
The German counterpart is the German Digital Library. Here you can
"find digitized holdings and indexing information from cultural and scientific institutions such as libraries, archives, museums, offices for the protection of historical monuments, media libraries as well as universities and other research institutions The DDB provides central access to digital images of books, documents and files, paintings, statues, installations, monuments, films and music."
(Source: German Digital Library)
In the German Federal Archives you can search for digitised contemporary documents from the following periods:
- North German Confederation and German Reich
- Federal Republic of Germany with Western Allied occupation zones
- German Democratic Republic with Soviet occupation zone