The answer is money. You are entitled to file an international patent application if you are a national or resident of a PCT Contracting State.The purpose of this guide is to provide you with basic information about filing a utility patent application with the USPTO. This tutorial will focus on patents and the process for securing a patent in the U.S. First, let's consider why we have a patent system? "WO" is a suffix to a patent number that indicates that the original patent application was filed under the Patent Cooperation Treaty. A priority claim is made to an earlierfiled patent application. For example, an Applicant can claim priority in a later-filed patent application. An international patent application must be prepared according to certain formal requirements set out in the PCT and its regulations. An inventor who wants to protect their invention in the U.S. needs to get a patent from the U.S. Patent and Trademark Office (USPTO).