There is a Plugin in Pressbooks called Hypothesis. It is activated for all our Pressbooks but it requires a few extra steps to set it up for your book.
First, create an account with hypothes.is.
Then in your book:
- Click Settings then Hypothesis
- Allow on Parts
- Allow on chapters
- Allow on front matter
- Allow on back matter
- Click Save Changes
- Then go to the View Site for your book.
- Click on any chapter pages etc and highlight some text to get the Annotate or Highlight options.
You can set up public groups or private groups etc in hypothes.is. You can create a group just with you in it to keep your comments private.
Enable annotation with hypothesis explains more.