Your best bet is to respect Facebook’s privacy settings and find alternative, honest ways to connect with the person.
If the profile is locked but the user has left the "Add Friend" button enabled (some do), send a genuine request. If they accept, you will automatically see their full-sized profile picture, cover photo, and posts. No viewer needed. fb locked profile dp viewer upd
When a Facebook user activates the profile lock, several restrictions are immediately applied to anyone who is not on their friends list: Your best bet is to respect Facebook’s privacy