It’s pretty much what it says on the tin! By clicking on the Restore Annotations option in the menu bar you can restore all of your deleted comments on a page by page basis. With comments which have had subsequent edits made to them, Restore Annotations will reveal the most recent version of the annotation, not the original.

Navigate to the File menu button on the top right-hand side of your screen.

Find the Restore Annotations option halfway down the window. The tool will reveal every deleted annotation on each page.
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Click Select/Select All then click Restore to restore the deleted annotations on your chosen pages.