You can sell your product for up to one year and then file a patent application with the United States Patent and Trademark Office. A stepbystep overview of a patent application and maintenance process.The five stages of a patent process. You may apply for a patent and sell your product to a buyer without licensing any rights (to your future patent) to the buyer. The easiest answer is: don't sell or offer to sell any product containing an invention until AFTER you file a patent application. Here you'll get answers to the basic questions about patents in the United States and foreign countries. We also provide inventor assistance resources. The onsale bar is part of Section 102 within patent law that can prevent an invention from being patented if it was sold prior to patent filing. When can I apply for a patent? Find out if you can produce and sell a patented product legally.