Aides to President Joe Biden have discovered at least one additional batch of classified documents in a location separate from the Washington office he used after leaving the Obama administration, according to a person familiar with the matter. Since November, after the discovery of documents with classified markings in his former office, Biden aides have been searching for any additional classified materials that might be in other locations he used, said the source, who spoke on the condition of anonymity to provide details about the ongoing inquiry.