The Annotation and Form Editor allows you to convert annotations and form fields to content elements. Once converted, the annotations and form fields are rendered as content in PDF document and cannot be edited. On saving the PDF document, the elements marked for conversion are removed and appear as a part of PDF content.

The below image shows 'Convert' button in Annotation Editor's properties panel along with the square annotation.

After conversion, the 'Convert' button is changed to 'Revert' button as shown in the below image. You can use the 'Revert' button to undo the conversion and make the annotation and form field visible and editable again.