WhatsApp has included a new feature in its latest app update – 'mark as unread'. This means that users can now mark messages as 'unread' even if they've been opened. That's so you can remind yourself to go back to a message if you don't have time to deal with it immediately.

What happens when you mark a message as unread?

Facebook has a feature that allows you to mark the messages as unread. ... The unread option will allow you to keep the message unread meaning it turns the seen message you received into the unread message. On your messenger, what you need to do is Tap and Hold on a chat and select the option Mark as unread.

Can someone see if you mark their message as unread?

no need to doubt.. whether you view the message and later mark as unread or you don't view the message at all but simply mark it as read.. either way it'll show 'seen' to the other person..