From : Blog Entry>>ILTA’s Blog Entry
Security – Adobe Acrobat Pro DC   To add password security to open a PDF document within Acrobat Open the PDF and click on  TOOLS   . Click on  Protect . The Protect toolbar displays. Click on the  Encrypt   drop-down. Choose  Encrypt   with   Password . Click  Yes   to change security if a prompt displays. Select the  Require   a   password   to open the document checkbox. Type a password in the  Document Open Password   field. Click on  OK .   To restrict [More]