If you need to duplicate the content of a page, the easiest way is to copy the page.
When you copy the page it'll need to be renamed if you intend to keep it in the same space – and Confluence will rename the page 'Copy of [originalPageName]' by default – as pages in a space must have unique names. If you plan on moving it to another space, you can keep the same name as long as you set the location while you're creating the copy. See Move and Reorder Pages for more information.