* Before doing encryption, Set a lock screen password by going to Setting 》 Security 》Screen Lock. Charge the battery fully and plug in your tablet.
* Encryption is irreversible and takes hours to complete. Duing the process, it will restart a few times. If you go to interrupt it, all data will be lost.
How to turn on encryption with Nexus 7
* From Home screen, touch Settings 》 Personal 》 Security 》Encryption 》 Encrypt tablet. Tap on "Encrypt tablet" button, type in your lock screen PIN or password, and then "Continue".
* Tap Encrypt tablet again to start encrypting.
* If you want to revert it to an unencrypted tablet, makeing a factory data reset.