cellphone
It depends... If you are using your wireless network for any activity which you do not want to share with anybody. You must have a password protected network.
pin is like a second password, adds more protection and prevents auto logins
PIN
password pin for receiver
If you know your password, you can reset your PIN, without having to type in your old PIN. If you forget your password or pin you can answer your security question and you can get into your account.
If you PDF file is password protected you need a password recovery software.
Change Your Password If That Happens
By entering the correct password.
By supplying the correct password.
Your Dell tablet is most likely running Windows 8. In order to put a password on your tablet, you must go under Settings, then Security. From there you will be able to set a PIN.
An accounts pin is specific to your account.