Saving as PDF with no editing capabilities should not allow you to edit
Currently, if you are working on an AI file, and then choose File / Save as / PDF (and select PDF output options that have NO editing capabilities), once the PDF is saved it then remains open.
The bug is, that although the PDF is set with no editing capabilities - the file will still allow you to make changes and add items outside the Artboard area.
The problem with this is that once you save and close. if you open the file again - there is no way to access the content outside the Artboard area.
So you could spend hours editing content outside the Artboard and then successfully save and close the file, without receiving any warning that you will lose content.
Solution: I suggest that if a file is saved as a non-editable PDF, that it should provide some type of warning either during post-save editing, or when trying to click a subsequent Save - that the content is not going to be usable.
I can’t think of a bulletproof method of preventing this. A message on save is an option, yep... but it’d be hard to tell if having stuff on canvas outside of the artboard is intentional or not. Still better than nothing.
As a workaround I advise to use Save a Copy method instead of Save As, in cases when you wish to continue to make changes into the original.