With OneNote for Windows 10, you can lock and unlock password-protected sections. To set a password, you'll need to use the desktop version of OneNote (such as OneNote 2013 or 2016).
Lock a section
To lock password-protected sections manually, right-click (if you're using a touch screen, tap twice) any section tab and then click or tap the Lock Protected Sections button on the menu that appears.
Unlock a section
Navigate to the section you want to unlock and type your password in the password field to unlock the section.
After unlocking a password protected section, you can view and edit its contents just like any other section, but to protect your privacy, page thumbnails aren't shown. The section will automatically lock if you don’t use OneNote for a few minutes.