When you work in a shared notebook, and someone else adds content, the titles of the workbooks, sections, and pages that changed become bold and the new content on each page is highlighted. This formatting lets you know there are updates to review and makes it easier to find the changes.
Note: This highlighting is different from the highlighting you can apply to text from the Home tab, even though it looks similar.
When you click a page, the bolding and automatic highlighting disappears, to show that you’ve reviewed it. However, you don’t have to click through each section or page one at a time to remove the highlights. You can mark sections and notebooks as read to remove the bolding and highlights at the same time.
To mark a section as read:
Click the section tab with unread content, and click History > Mark as Read.
Select Mark as Read.
You can also mark the entire notebook as read. From the History tab, click Mark as Read, and then click Mark Notebook as Read.
Tip: If you want to reapply the bold and highlighting on a page, as a reminder to look at it later, click Mark as Read > Mark as Unread.