The act of notarization doesn't make a document legally binding, and it simply certifies that the individuals who sign a document are who they purport to be, according to the National Notary Association. Although a legally binding document requires signatures from all the involved parties, not all documents need notarization.
The National Notary Association explains that notarization includes three factors. These include the acknowledgement, or identification of the parties to the document; jurats, which require that the parties sign the document and affirm the truth of their statements; and certified copies, which verify the validity of reproductions of the original document.
A legally binding document is one that can be defended in court. A valid contract, for example, is legally binding on both parties. Signatures symbolize the parties' acceptance of the terms, but it's the acceptance itself that provides the contract's validity, according to the U.S. Small Business Administration.