While Save As is a useful tool for creating a new copy of a project so you can slightly modify the new copy, sometimes you may want only a few pages of an existing project copied into a new one. For that, we have the Import/Copy Pages function.
When clicking on the Add Pages button, you'll see this option. Once you select it, you'll be taken to a new menu.
From here, you can select the project that you wish to copy pages from, and those pages will then be displayed below. Simply click on the page(s) that you wish to import and select the Import button. This will then place your selected page into your project, prior to the pages that you are currently on in Edit mode.
If more pages need to be selected, you can repeat this process. Once finished, you can use the Page Sorter feature to move the pages around in the project.