Instead of going through Insert > Bookmark, you can use this guide to get the job done. How to show or hide all Bookmarks at once in Word ...

A long or complex document can be difficult to navigate. Susan Harkins explains how Word's bookmarks can help.

Fix Bookmark not Defined in Microsoft Word You can fix Bookmark Not Defined or Error, Reference source not found problems when you update a field that has a broken link to a bookmark in Word.