Possible Clues:

• Secret-protecting docs
• Confidentiality docs
• Secrecy contracts, for short
• Docs that leave people speechless?
• Legal documents to ensure confidentiality, briefly
• Secretive contracts, briefly
• Secret-protecting documents: Abbr
• Leak preventers, of a sort: Abbr
• Contracts of confidentiality, briefly
• Confidentiality contracts: Abbr