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The -pdfencrypt option turns on the encryption for a PDF file.  If the option -pdfownerpass, -pdfuserpass, -pdf128, or -pdfpermit are present, encryption is automatically turned on without specifying -pdfencrypt.  By default, encryption is turned off.


An encrypted PDF file is one where most of the contents of the PDF file are encrypted, and requires decryption for an application to interpret the contents.   An advantage of an encrypted PDF file is that changing the contents of an ecrypted PDF file using a binary file editor, for example, is virtually impossible without corrupting the entire PDF file.  On the other hand, with an unencrypted PDF file, changing the contents (for example, the Creator or Author fields) is trivial with a binary file editor.


If the -pdfencrypt option is used with no other encryption options, the default is as follows:


No user or owner password.  This allows the document to be opened in Adobe Acrobat without specifying a user or owner name.
The encryption uses a 40-bit encryption key (as opposed to a 128-bit encryption key).
The permissions are to not allow any modifications to the document.


Default Setting:

No encryption is done if no other encryption options are specified (-pdfownerpass -pdfuserpass, -pdf128, or -pdfpermit).