how to delete annotations in preview

I have no issue removing annotations from saved PDF documents on Catalina 10.15.1. Annotations that you apply to images in Preview are permanent though.

Apple omitted the Preview Inspector tool as a default toolbar item. From View menu : Customize Toolbar… drag and drop the Inspector tool onto your Preview toolbar.

With an open, annotated PDF, select the Inspector tool, and on the right-most tab in its resultant floating window, you will see a ordered list of annotations by page. Clicking on any annotation in this list will also select it in the PDF, where you can simply press the delete (backspace key) to remove that specific annotation. There is no undo.

Hello vxiansheng, 

Thanks for reaching out to the Apple Support Communities. I see that you're interested in learning how to edit photos and PDFs which have been marked-up. 

This article contains the steps to follow to change a marked-up photo, if you did so in Photos: Use Markup to write or draw on a photo in Photos on Mac. 

"To change a marked-up photo later, select it, then click the Extensions button and choose Markup again." 

Any items which were added from Preview, you can select the item then remove or edit it. I tested on my Mac (running macOS Mojave) by opening a PDF in Preview, adding some mark-up boxes, and saving the changes that I made. I then opened the same file in Preview, and was able to remove the mark-ups. 

If you were working in the Quick Look or Quick Actions window, your changes can not be undone after you close the window. Mark up files on Mac. This article will tell you more about Quick Look: View and edit files with Quick Look on Mac. 

All the best.

Hi vxiansheng,

Glad to hear that you were able to get it all sorted out! If you have any questions down the road, we're only a message away.

Enjoy the day!