PDF (Portable Document Format) file format was launched by Adobe Systems in 1993 to provide user the facility of document sharing electronically. PDF is a universally compatible file format which runs on all computers irrespective of their platform. In the early years of its launching, use of PDF file was rare but implementation of new features have made it very popular. Now most of the organizations and corporations use PDF to send documents electronically. Encryption is one of the most important features which make PDF very popular. PDF allows user to set password when he want to send confidential and sensitive information over internet. User can set two type of password on a PDF file:
Document Open Password (User Password) - This type of PDF password restrict unauthorized user from opening the PDF file.
Permission Password (Master Password) - PDF master password restrict unauthorized user from editing, copying, printing the content of PDF file.
You can set user password or master password according to the need of user who will be receiving the PDF file. You can follow the steps (given below) to set password on your PDF file.
1. Open the file with Adobe Acrobat.
2. Go to file menu -> Document Security.
3. In ‘Document Security’ dialog box select ‘Acrobat Standard Security’.
4. In ‘Standard Security’ dialog box check both (according to you need) the boxes "Password Required to Open Document" and "Password Required to Change Permissions and Passwords" and enter desired password in the boxes.
5. After entering both passwords you can set encryption level either 40-bit RC4 or 128-bit RC4 (for 128-bit encryption level user must have at least Acrobat Reader 5.0 version or more).
6. Below encryption level drop down menu you can select different restriction permissions like 'No Printing', 'No Changing the Document', 'No content copying or Extraction, Disable Accessibility' and 'No Adding or Changing Comments and Form Fields'.
7. After selecting desired restriction permission click "OK" button.
8. You will see a window asking you to 'Confirm the Password to Open the Document'. Enter 'Document Open Password' and click 'Ok'.
9. Again you will see a window asking you to 'confirm the Password to Change Security Setting'. Enter 'Permission Password' and click 'Ok'.
Now your PDF document is password protected and safe.
While selecting the encryption level (in step 5) you should keep in mind that 128-bit encryption is much stronger than 40-bit encryption. So if your PDF file contains highly secret and confidential information then you should use 128-bit encryption. It is interesting to know that there are many PDF password recovery tools which can easily crack both 40-bit and 128-bit encryption level passwords. So by enabling password on your PDF file you can prevent unauthorized access from human but still password is recoverable by PDF password recovery tools.