A PPTX file or any of the new file formats that Office 2007 and later use such as POTX or THMX are different than the older binary file formats such as PPT. That’s because these new file formats that end with an “X” are essentially XML based file formats.
Even more interesting is the fact that the actual file is not an XML based file but only a wrapper that contain many disparate and related XML based elements. The wrapper technology used is just simple ZIP technology. If you want to edit Office XML files, you will therefore need to unzip, edit, and finally zip the file. Alternatively, you can perform XML Editing within Visual Studio 2010.