You can decide whether to remove all annotations, remove annotations on a page, or export annotations to retrieve them later.
Thanks for using Xodo and your feedback! You can remove annotations, remove annotations on a page as described here: http://feedback.xodo.com/knowledgebase/articles/852894-deleting-an-annotation. In addition, you can export summary of annotations as described here: http://feedback.xodo.com/knowledgebase/articles/843852-exporting-summary-of-annotations.
Hope it helps!