Restrict Editing is selected by clicking on the Protect group of the Review tab.
Select Stop Protection by clicking on the Restrict Editing task pane.
If a password request is made of you, type it.

Click File > Info > Protect Document and select Restrict Editing

Unlock a protected document

1. On the Review tab, in the Protect group, click Restrict Editing.
2. In the Restrict Editing task pane, click Stop Protection.
3. If you are prompted to provide a password, type the password.