A few things that would improve this.

Auto-updating the viewer's side of the document after you save the document instead of refreshing it every time or having to update the link.

When they comment/draw on that it shows on the designer's side in the application as a popup on the document that they can add a checkmark afterward or comment if needed. This would basically bridge both ends to see live updates and live suggestions in the application and on the viewer's side.

It would also make the designer's life easier to go between tabs or applications to see the edits wanted.