You can use the free PDFGear app to encrypt a PDF. Open the PDF file in the program and click the Tools tab at the top of the window. Now, click the Password icon, enter and, in the Set Password box, ...

Opening a PDF file with the password can be challenging since you can't unlock it without remembering a password.

Password protecting a sensitive PDF file is a great way to secure its contents from prying eyes. However, sharing a password-protected PDF can be a logistical nightmare, especially if the contents ...

With the file open in Pages, Numbers, or Keynote, select File and then Set Password to choose and apply your password.