Working PDF, Note, comments (Reason and label) icon, and numbering title
If you can develop the icon of PDF and Note as a working icon, so If we click on those icons the information will come like a pop-up window for notes and a new page for pdf or you can allow using an extension like adobe reader or others to read those pdf, also if we can add pdf file directly by dragging them from our PC, will also be helpful.
For creating a comment on a specific article if you active those buttons where we can edit or delete by double-clicking or right-click on the mouse.
A serial number on each and every title will also help us to identify, remember and discuss the title among reviewers.
All these changes will save our time and make our work more enjoyable, from my perspective.