classified document; confidential document
Refers to official documents whose disclosure is restricted, typically in government, military, or corporate contexts.
This classified document cannot be taken out without permission.
Handling confidential documents requires the utmost care.
秘密文書 is a broader term for any secret document, while 機密文書 specifically implies official or state secrets with legal protection.
Compound of 機密 (classified, secret) and 文書 (document). The exact historical derivation is uncertain, but the meaning is transparent from its components.