Confidentiality And Nondisclosure Agreement If One Puts A Nondisclosure Agreement On A Business Plan, Is It Legally Effective, Or Are Signatures Required?

If one puts a nondisclosure agreement on a business plan, is it legally effective, or are signatures required? - confidentiality and nondisclosure agreement

In other words, by reading this document, you agree to the confidentiality ... ... etc "on the first page of a business plan actually legal? Does this mutual agreement for legal purposes in the contract? Or is this value, and a separate written, NDA is the only way?