After adding a document folder to a transaction, from your right side panel, click the Upload button to have your file stored in the system.

From the Document Folder, click the + File button, enter the file name, and click Add. Click the Upload button to have your file stored in the system. The Placeholder File (+ File) is a place where you can put your files inside your document folder.

Once the document is uploaded to your folder, you can change the file by clicking on the drop-down button, clicking Toggle Notes, and the Replace button. The original document will not be stored anymore, and it will only keep your replacement document.