Because one file in your Stockpress workspace can live in multiple Collections, you can add a file that lives in one Collection, to another Collection, without duplicating it.
To add a file or files to another Collection, hover over the file(s) and click the ‘+’ icon either on the file view or in the action bar at the bottom of the screen. This will bring up a modal where you can choose the Collection that you want to add it to.
Type the name in the field and click the ‘Add’ button. If the Collection does not exist, you can click the “+ New Collection” button to create a new Collection.
You can also add files to Collections with Collection Preview. Find out how here.
You can also move files from one Collection to another. Find out how, here.