1. Open a PDF in PDF Reader.
2. Click “Security” from the main menu bar.
3. Choose “Encrypt” from the menu, and then you will be brought to a window where you can select the encryption settings.
4. Select the output folder where you’d want to save the newly encrypted PDF file.
5. You may also add more PDF files to encrypt by clicking on “Add Files”.
6. Depending on how secure you want to encrypt the PDF, you can add a password to it to secure the content from being viewed, copied, and printed.
7. Then press the “Encrypt” button to start the encryption.
8. The new password-protected PDF will be saved in the output folder.
9. Or you can switch to the "Home" tab and click on the “Encrypt PDF” entrance under the office toolset section.