A written declaration made on oath in the presence of a magistrate

One word substitute is Affidavit.

Voucher: a small printed piece of paper that entitles the holder to a discount, or that may be exchanged for goods or services.
Dossier: a collection of documents about a particular person, event, or subject.
Affidavit: a written statement confirmed by oath or affirmation, for use as evidence in court.
Document: a piece of written, printed, or electronic matter that provides information or evidence or that serves as an official record.