How Does PDF Encryption Work?
A PDF offers several layers of security to encrypt a file so only an authorized user can open and read it. Even with authorized users, you can limit their abilities to edit, print and other options to prevent them from propagating readable copies to others. While no encryption is foolproof, the creator of the PDF file can set the level of security based on the perceived threat. You set the security level in the “Document Properties” box.
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Algorithms
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Encryption uses an algorithm to scramble the contents of a file. To unscramble the file, the user needs a key. Different security levels come with a higher level of level of encryption, shown by the higher bit numbers used in the algorithms. The higher the bit number means the tougher it is for a hacker to break the code.
Passwords
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You can set a password to encrypt the entire content of the PDF. With this setting, search engines will not even be able to access the PDF’s metadata. You can set the password to be compatible with Acrobat 3 or later, but that only carries a 40-bit encryption. Setting compatibility in any security level for Acrobat 7 and later raises the bit encryption to 128, and for Acrobat 9 and later, 256. Options include encrypting the document but leaving access to metadata open to search engines, or encrypting only file attachments. The latter creates a security “envelope” to give access to attached files only to authorized users.
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Restrict Uses
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With a separate password, you can restrict a user’s ability to print and make changes in the setting. A password can allow either low or high resolution printing. A password can allow a user to make limited changes to a PDF, including filling in form fields, electronically signing signature fields and adding comments. The password settings also let you enable or prohibit copying of the PDF contents. You can use a password to restrict the changes a user can make even if you don’t require a password to open the PDF.
Certificate Security
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Certificate security restricts access to the PDF file to a set list of e-mail recipients you designate when setting the security level. It’s a higher level of security since you don’t send around passwords. As with passwords, you can set different permission levels on changing the document for each recipient.
Store on a Server
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When you send a PDF to a restricted server, only a set list of recipients who have access to the server can view the document. The security is similar to a certificate security except you never send the PDF to other users. This makes it less likely for hackers to intercept the file.
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