Encrypting your Adobe PDF files will add security to images and documents such as portfolios, confidential business files and Mom's famous apple pie recipe. Adobe features include the ability to secure documents from being opened, printed or edited and from copying text and images. Encrypting your files can also have drawbacks, such as forgetting your password and not being able to open them in a "Read Only" mode.
Open the PDF and click on "Advanced "Security" on the main menu, click on "Password Encryption" from the pull-out menu and then Click "Yes" to the security change prompt screen.
Click the check box next to "Require a Password to Open the Document" and enter your password in the "Document Open Password" text box. Click "OK" to accept and then enter your password again to confirm and then click "OK." Save your file for the change to take place.
Click the "Required Password to Change Permissions or Password" to have the user enter a password to make any changes to the security of the file; type in a password that is different from the "Password to Open the Document."
Click the "Printing Allowed" pull-down menu and choose "Low Resolution" (150 dpi) to allow users to print bitmap images or choose the "High Resolution" option to allow users to print high-quality vector outputs.
Remove a password by opening the PDF and entering the password when prompted, then hit "OK." Click on "Advanced," "Remove Security," "Password Encryption" and then "OK" on the "Are you sure you want to remove security from this document?" prompt screen. Save your file for the change to take place.
When using the "Restrict Editing and Printing of the Document," the user will not be able to open the file in a "view-only" format, but will be able to open with the password in Illustrator, Photoshop or InDesign.
Keep a backup of your PDF file. If you forget the password, there is no way to recover it.