With Protector you can hide any part of posts and pages askeing user to "do some action" to reveal it.
Protector can hide on pages and posts part of the content, displaying an alternative message. The message can ask the user to "do some action" like click a link or subscribe a newsletter.
The hidden part will be revealed accessing the page or post with a special secret key you send the user, eg. after subscription.
See the plugin official page for more.