OneNote for Windows 8 lets you apply password protection to confidential notes.
Note: Make sure you're running the latest version of OneNote to get these features.
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.
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 app bar that appears along the bottom of the screen.