Toolbar choose Protection > Encrypt > Encrypt with Password.
If you receive a prompt, click OK to change the security.
Select Require A Password To Open The Document, then type the password in the corresponding field. For each keystroke, the password strength meter evaluates your password and indicates the password strength.
Key in the password again.
Toolbar choose Protection > Encrypt > Remove File Open Password
Two categories of passwords are available:
File Open Password
A File Open password (also known as a user password in pdf specs) requires a user to type a password to open the PDF document.
File Permissions Password
A permissions password (also known as a master password defined in PDF specs) requires a password to change permission settings. Using a permissions password, you can restrict printing, editing, and copying content in the PDF. PDF readers don't need a password to open the document in PDFw or other PDF reader software. They do need a password to change the restrictions you've set.
If the PDF is secured with both types of passwords, it can be opened with either File Open Password or File Permissions Password. However, only the File Permissions Password allows the user to change the restricted features.
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