case file; dossier; all documents related to a case
Refers to the complete set of papers and documents concerning a particular matter, often used in legal, administrative, or investigative contexts.
The lawyer submitted the case file to the court.
This dossier contains all the records of the case.
書類 is a general term for documents or paperwork, while 一件書類 specifically means the complete set of documents for one particular case or matter.
ファイル is a broader term for any file, including digital ones. 一件書類 is more formal and typically refers to physical or official case documents.
Compound of 一件 (one case/matter) and 書類 (documents). The exact historical derivation is uncertain, but the meaning is transparent from its components.