Password Protect lets you easily hide content in any post or page behind a safe and secure password. No complex membership system required. Simple Password Protection Just select the content you’d like to hide (it can be a video, audio track, paragraph, answer or anything else at all), click on the lock button and select a password that must be entered. Once activated you’ll see a nice new ‘Password Protect’ icon added to your Visual editor that you can use to password protect selected content.

https://premium.wpmudev.org/project/password-protect-selected-content/