Hi Siva,
Portfolio Item Deep Copy will help you copy Stories and Tasks along with Features. Follow the below steps using the app:
Ensure you put the below copy application in full-screen mode (arrows on the right side of the title bar) before you start the process so you see the list of work items properly.
Ensure you are in the project from which you want to copy (the current project) when you execute the deep copy.
Ensure you have at least Editor access to both the current and target projects otherwise the copy will fail.
Once you select the work item to copy, it will take a couple seconds for the copy button to become active. Then you can press it.
Hope this helps
Thanks
Priyanka