There are ways to end up with mystery stuff on slides. Items that cannot be seen, edited or deleted by normal means – invisible elements. One add-in that I have used extensively is PPTXtreme’s Soft Shadow. It has provided photoshop quality shadow effects to PowerPoint since XP. The coding behind it is incredible too. To allow an object to be restored to its original, non-shadowed, state it turns the original shape invisible. So it is there, but not really there. The Soft-Shadow add-in has a great set of management tools to remove unneeded invisible elements (especially to keep file from becoming large).
So, for our purposes I am using the Soft-Shadow add-in to create an invisible element on a slide to discuss the Inspect Document INVISIBLE ON-SLIDE CONTENT feature.
Here is my sample slide. I inserted a circle autoshape and then applied the drop shadow with the PPTXtreme Soft-Shadow add-in.
Open the Document Inspector (OFFICE BUTTON >> PREPARE >> INSPECT DOCUMENT)and have it check for INVISIBLE ON-SLIDE CONTENT.
It reports there is a hidden object on slide #1 (the one I purposefully added).
After running the clear option, reinspect and now the presentation has no extraneous mystery items!
– Troy @ TLC