It is important to recognize that a nondisclosure agreement (NDA) has certain inherent limitations. First, a NDA is binding only on the party who signs the agreement and generally does not protect against third-parties making, using, selling, or disclosing your invention or trade secret. Second, a NDA protects your invention and trade secret only so long as the invention or trade secret remains a secret. Publicly disclosing or selling your invention will render the NDA unenforceable under applicable trade secret law.
A patent provides broader protection without the limitations of a NDA, but the invention must be eligible for patent protection and the process to obtain a patent is slow. Combining a NDA with a pending patent application is generally the best way to protect your invention.