Encrypting PDF Files

The last and most secure type of security that you can add to your PDF documents employs the Certificate Security system that you use to digitally sign documents, along with the list of Trusted Certificates in your user Digital ID file. When you encrypt a PDF document with Certificate Security, no one has access to the document other than those you specifically designate as recipients, and you can designate as recipients only those persons who are already on your Trusted Certificates list.
The steps for encrypting a PDF document with Certificate Security are as follows:

1. Choose Document➪Security➪Encrypt for Certain Identities Using Certificates. The Restrict Opening and Editing to Certain Identities dialog box opens.
2. In the Identity Directories list box, click the name of the person you want to add to the Recipients list box below, and then click the Add to Recipient List button.
3. Click the name of the newly added recipient to highlight it in the Recipients list box.
4. Click the Set Recipient Permissions button. By default, Acrobat grants the recipient full access to the PDF document whose user permissions include general editing, commenting and form field authoring privileges, the ability to print the document at any print resolution, and full copying and extraction privileges.
5. To restrict the recipient’s user permissions in some way, click the Restrict Printing and Editing of the Document and Its Security Settings button.
6. Limit the permissions by deselecting the Enable Text Access for Screen Reader Devices for the Visually Impaired check box and/or the Enable Copying of Text, Images and Other Content check box and/or by selecting new options in the Changes Allowed and Printing Allowed drop-down lists before you click OK.
7. Repeat Steps 3 through 6 (as they apply) to add your other recipients from the Identity Directories list box and set their user permissions in the Recipients list box.
8. After you’ve added all the recipients and set their user permissions, click the OK button. If the Certificate Security - Alert box appears, telling you that settings will not be applied until you save your PDF document, click OK. You can also opt to not show this dialog box in the future by selecting the Do Not Show This Message Again check box before you click OK.
9. Choose File➪Save to save the Certificate Security encryption settings for the current document. Alternatively, choose File➪Save As and edit the filename and/or folder location of the encrypted document before clicking the Save button. After you save your PDF file encrypted with Certificate Security, you can distribute copies to all the people you added to the Recipients list. When someone on the list tries to open the encrypted file, Acrobat displays the Select My Digital ID File dialog box, where the user selects his or her user Digital ID and enters his or her user password. When the user clicks the OK button to close the Select My Digital ID file dialog box, Acrobat checks the user’s public key against the certificate information (specifically the MD5 and SHA-1 fingerprints) in the encrypted file.

When Acrobat finds they match, it then opens the PDF document. The user then has access to the opened document according to user permissions that you set. To check these permissions, the user can right-click (Control+click on the Mac) the Document Encrypted key that now appears on the Document pane Status bar (a locked padlock on the left of the Status bar), select Document Security on the context menu, and then click the Security Settings button in the Document Properties dialog box.
If someone not on the Recipients list attempts to open a PDF document that’s encrypted with Certificate Security, upon logging in, he or she will receive the Certificate Security - Alert dialog box with the message You do not have access rights to this encrypted document. When the user clicks OK to clear this dialog box, the document will fail to open.