One more thing, already touched on, is the undo function. Allow multiple step undo and redo.

Repair it, so that it does not become confused as the previous contributor suggested. But also add multiple step undo and redo.

P.S. Farther down the line in your list of improvements, Allow pictures to be double clicked and sent to editor of choice for editing and then return into the document with edits complete. Maybe liimited to more simple programs like Irfanview if higher end products are too difficult to interface with, or partner with a spedific editor, or develop your own.