An NDA does not necessarily need to be witnessed, but it is recommended to have a witness present during the signing of the agreement to further strengthen the validity and enforceability of the contract.
Not all contracts need a witness. For example, a simple agreement between two parties likely will not need a witness, although it is in your best interest to have one. However, certain contracts will need a witness. For example, a deed or a will both need witnesses.
A deed may be validly executed by an individual if it is signed at their direction and in their presence and the presence of 2 witnesses who each attest the signature (section 1(3)(a)(ii) of the Law of Property (Miscellaneous Provisions) Act 1989).
Outline how you will handle disagreements or misunderstandings. Agree to celebrate each other's achievements and special occasions. Specify if this is a temporary agreement or ongoing. Include a clause that allows for changes to the contract as the friendship evolves.
Just like wills, there is generally no requirement that a contract be notarized in order to be legally binding. However, if a party who signed a business agreement decides to dispute that agreement in court, a notarized contract can help a great deal.