langchain/document_loaders/blackboard.py/BlackboardLoader/_load_documents
class BlackboardLoader:    def _load_documents(self) -> List[Document]:
        """Load all documents in the folder.

        Returns:
            List of documents.
        """
        # Create the document loader
        loader = DirectoryLoader(
            path=self.folder_path, glob="*.pdf", loader_cls=PyPDFLoader  # type: ignore
        )
        # Load the documents
        documents = loader.load()
        # Return all documents
        return documents