With the page open in Contensis, Save (Create a Copy) will create a new page in the project explorer that is a copy of the page and it will have a file name to that effect.
Your original page will still exist. Editing the original will then update all the shadow copies.
To create a copy of a web page:
With the page open in the editor
Contensis will save this copy in the same folder as the original or you can choose an alternative.
If you do try and edit a shadow copy you will see a warning screen.
Create Copy can also be selected from the project explorer menu: