When I rename a zip file to a ztd file I see it as filename.zip.ztd
When this happens it is because the file extensions 9ie .zip .ztd are hidden from your view. To enable the file extensions to be seen :
1) open windows explorer
2) click on tools in the menu bar
3) click on folder options
4) click on the View tab
5) scroll to and uncheck the box beside - Hide extensions for known file types
diong this will allow you to see the file extensions .zip & .ztd and make it easier to change them.