PDF Security and permissions are able to allow the creator to retain control of the document and associated rights.

PDF has two protection features that will be utilized, individually or with each other, in any document:

The document could be encrypted so that only approved consumers can accessibility it. There is separate authorization for that owner of the document and for all other consumers; the users' entry can be selectively limited to allow only specific operations, for example viewing, printing, or editing.

The document might be digitally signed to certify its authenticity. The signature could take numerous forms, such as a document digest that has been encrypted with a public/private key, a biometric signature like a fingerprint, and others. Any subsequent adjustments to a signed PDF file invalidate the signature.

PDF's regular safety handler enables entry permissions and up to two passwords to become specified to get a document: an operator password and a person password. An application's decision to encrypt a document is based on regardless of whether the user making the document specifies any passwords or accessibility restrictions (as an example, inside a safety settings dialog box that the consumer can invoke before saving the PDF file). In that case, the document is encrypted, and the permissions and details required to validate the passwords are stored inside the encryption dictionary. (An software may possibly also produce an encrypted document without having any user interaction if it has another supply of details about what passwords and permissions to use.)

If a consumer attempts to open an encrypted document that features a person password, the software ought to prompt to get a password. Properly supplying both password allows the user to open the document, decrypt it, and exhibit it on the display. In the event the document does not have a person password, no password is requested; the application can just open, decrypt, and show the document. Regardless of whether additional operations are allowed on the decrypted document depends upon which password (if any) was supplied once the document was opened and on any access restrictions that were specified when the document was produced:

Opening the document together with the right operator password (assuming it is not the identical as the person password) permits full (proprietor) access to the document. This unrestricted access consists of the ability to alter the document's passwords and access permissions.

Opening the document with the correct user password (or opening a document that does not have a person password) enables extra operations to become done according to the user entry permissions specified in the document's encryption dictionary.

Access permissions are specified in the form of flags corresponding towards the numerous operations, as well as the set of operations to which they correspond depends on the safety handler's revision range (also saved in the encryption dictionary). In the event the revision quantity is 2 or greater, the operations to which user access could be controlled are as follows:

Modifying the document's contents.
Copying or extracting text and graphics from the document, such as extraction for accessibility purposes.
Adding or modifying text annotations and interactive form fields.
Printing the document

If the protection handler's revision range is three or higher, user accessibility for the following operations may be controlled much more selectively:

Filling in forms (that's, filling in existing interactive kind fields) and signing the document (which quantities to filling in current signature fields, a kind of interactive kind subject).
Assembling the document: inserting, rotating, or deleting pages and developing navigation elements for example bookmarks or thumbnail images.
Printing to a representation from which a faithful digital duplicate with the PDF content could possibly be generated. Disallowing such printing might lead to degradation of output good quality (a function implemented as "Print As Image" in Acrobat).

Additionally, revisions 3 and greater enable the extraction of text and graphics (in support of accessibility to consumers with disabilities or for other functions) to be controlled individually.

If revision four is specified, the standard safety handler supports crypt filters. The assistance is limited to the Identification crypt filter and crypt filters named StdCF whose dictionaries contain a CFMvalue of V2 or AESV2 and an AuthEvent worth of DocOpen.

Notice: Once the document has been opened and decrypted effectively, the application has access to the whole contents of the document. There is certainly nothing inherent in PDF encryption that enforces the document permissions specified within the encryption dictionary. It can be up to the implementers of PDF consumer apps to respect the intent with the document creator by limiting person entry to an encrypted PDF file according to the permissions contained within the file.

Be aware: PDF 1.5 introduces a set of entry permissions that don't call for the document to become encrypted.

Every document has a "trailer dictionary" which holds references to a few important things (like the tree of page objects which contains the document content) and optionally to an encryption dictionary.  If the encryption dictionary is present (i.e., if the document is encrypted), it contains the information needed to decrypt the document.  An example:

    % Trailer dictionary
    trailer
    <<
        /Size 95         % number of objects in the file
        /Root 93 0 R     % the page tree is object ID (93,0)
        /Encrypt 94 0 R  % the encryption dict is object ID (94,0)
        /ID [<1cf5...>]  % an arbitrary file identifier
    >>

    % Encryption dictionary
    94 0 obj
    <<
        /Filter /Standard   % use the standard security handler
        /V 1                % algorithm 1
        /R 2                % revision 2
        /U (xxx...xxx)      % hashed user password (32 bytes)
        /O (xxx...xxx)      % hashed owner password (32 bytes)
        /P 65472            % flags specifying the allowed operations
    >>
    endobj

There are two type of passwords available, "user password" and "owner password":

Document open password With a document open password (also identified as a user password), customers need to sort in the password you specify to open the PDF.
Permissions password Whenever you set only a permissions password (also recognized being a grasp password), recipients don't want a password to open the document. However, they ought to type the permissions password to set or alter the restricted capabilities.

If the PDF is secured with each sorts of passwords, it may be opened with possibly password. Nevertheless, only the permissions password makes it possible for the person to change the limited functions. Because from the added safety, setting each types of passwords is typically helpful.

VeryPDF PDF Security software does support batch encryption, you can use command line application to encrypt your PDF files by following steps,

1. Create a file list for all of your PDF files from DOS Command Line window by following command line,

dir C:\test\*.pdf /s/b > C:\files.bat

2. Open "C:\files.bat" in notepad.exe and and replace "C:\" with "encryptpdf.exe -i C:\" keyword,
~~~~~~~~~~~~~~~~~~~
encryptpdf.exe -i C:\test\001.pdf -o C:\out\001.pdf -w owner -u user -e 40 -p
encryptpdf.exe -i C:\test\002.pdf -o C:\out\002.pdf -w owner -u user -e 40 -p
encryptpdf.exe -i C:\test\003.pdf -o C:\out\003.pdf -w owner -u user -e 40 -p
encryptpdf.exe -i C:\test\004.pdf -o C:\out\004.pdf -w owner -u user -e 40 -p
encryptpdf.exe -i C:\test\005.pdf -o C:\out\005.pdf -w owner -u user -e 40 -p
......
......
......
~~~~~~~~~~~~~~~~~~~

3. Run "C:\files.bat" to do the batch conversion.

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