I guess I found a workaround... I cannot show the whole code involved but something along those lines:
I have a
Treeview that stores an absolute path
abs_path of different documents... Now, I just check if one of these filepaths is in my open documents paths via:
def get_all_docs_paths(): all_docs_paths =  first = c4d.documents.GetFirstDocument() while first: folder = first.GetDocumentPath() abs_path = os.path.join(folder, first.GetDocumentName()) all_docs_paths.append(abs_path) first = first.GetNext() return all_docs_paths
If yes, the document is open, if not it is closed.