In order to open the file you need to have greenstreet Publisher installed on your computer. Since the application has been discontinued, you can try to find it on Amazon, eBay or other similar websites. Also, you need to know that the software can run only on Windows XP and below platforms. Alternatively, you can try opening the files using Desktop Publisher Pro or Publish-it software.
Note: If you have the greenstreet Publisher software installed on your computer and the file is not opening, try reinstalling the application.