Once you have added a number of sources with their attachments, you have to keep track on a separate document/notebook what you have processed and what you have not. Furthermore, often after reading a certain pdf you still know that you have to return to it, but there is no way of quickly making a note for yourself. If there would be a mail-like indication system that shows unread entry titles in bold, or otherwise indicates them, that would be enormous help! In addition, there could be a reading list shortcut folder where one could place links to the PDFs and reorder them.