You can get to this page by clicking Unread in the menu panel on the left side of the page. This page contains all of the documents that has not been read/reviewed yet, regardless of what stack they are in. You can right click on a document and select Mark as read which will remove the document from this page. You can also select multiple documents by holding down the Shift key and selecting the documents you want.
NOTE: When you mark a document as red, a green checkmark will appear at the bottom right corner of the image thumbnail.
NOTE: If you click the 3 vertical dots in the top right corner of the page, you can select/deselect all documents.