Click on the highlight or sticky note, and then right click your mouse for options. Choose “Delete Annotation” at the bottom of the popup window and you will remove the selected highlights or the sticky note.
Make sure you DO NOT click “Remove”. Clicking “Remove” will remove the PDF article from your reference. In case you accidentally removed the PDF article from the reference, you just click on the “NO” button to the question “Do you want to save the changes you made to the reference?” when you close the record.
Do not choose “Hide Notes/Mark-up” either, because it will hide all the sticky notes and highlights. Keep “Show Notes/Mark-up” enabled.