If you have mark up on a document, image, PPT slide deck, etc., you can remove the mark ups without deleting the content.
In the white board tools there is a slection tool.
You can use that tool to select one or multiple objects on the whiteboard overlay of whatever you are sharing. Click and drag to create a selection box around all the markups you not longer want. Then you can use the Delete key on your computer or the trash can icon in the Whiteboard tools to remove the selected items.
It should be noted that you will need to do this for each slide in a PPT deck that has been marked up or on each page of a PDF document. Each one gets a unique whiteboar overlay for each page/slide.
Alternatively, you can re-upload the object and the new instance of the document won't have the whiteboard mark ups on it. Which ever path is the path of least resistance is the best for you.