You can assign a password to a document so that only those who know the password can open the document. Passwords can consist of almost any combination of numerals, capital or lowercase letters, and special keyboard characters.
A document can have only one password. If you change an existing password when you share a document with others, the new password replaces the original.
Important: There’s no way to recover your password if you forget it. Be sure to choose a password you won’t forget, or write the password down in a safe place.
Choose File > Set Password (from the File menu at the top of your screen), enter the requested information, then click Set Password.
Select the checkbox if you want to add the password to your keychain.
If you add a password after you share a document, be sure to notify participants.
Note: Adding a password to a document doesn’t encrypt the file.
With the document open, do one of the following:
Change a password: Choose File > Change Password (from the File menu at the top of your screen). Enter the requested information, then click Change Password.
A document can have only one password, so if you change the password when you share the document, that becomes the document’s only password.
Remove a password: Choose File > Change Password. Type the old password, then click Remove Password.
If you add a password to a document, or change an existing password, it applies only to that version of the document and to subsequent versions.
If the document is shared, to prevent others from restoring an unprotected version of the document or a version with an older password, stop sharing the document, add a unique password to it, then share the document again.