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1. Several important concepts

Global encryption keys, referred to as the global key, used to generate object encryption key.

Object encryption keys, referred to as the object of keys, is used to actual encryption PDF files content keys, different from the retrospection of the PDF of the simulation of the encryption all share a key different object, PDF files of each object encryption key is not the same.

The User Password User Password.

Password access sites password.

2．PDF file encryption process

In an article introduced roughly about ACROBAT PDF encryption and encryption of PDF files to create the encryption dictionary object. And we put forward the following four questions:

1. The content of the document is how to be encrypted?

2. Encryption keys are how to generate?

3. Encryption of each a dictionary is how to generate?

4. Encryption dictionary and the relationship between the encryption key?

The first question is our ultimate goal, this paper will ultimately have to solve this problem is.

The following is a PDF file encryption the general process:

1. Choose PDF compatible version and input user password, authority password.

2. According to the input to generate encryption dictionary object.

3. By the input and encryption key generated global dictionary object.

4. The global key will generate the object encryption key.

5. Use object encryption key to encrypt content object.

6. Produce of the original keys

char temKey = Test[32];

unsigned int keyLength = length/8;

for (i = 1; i <=19; i++)

{

for (j = 0; j < keyLength; ++j)

{

tmpKey[j] = fileKey[j] ^ i;

}

rc4InitKey(tmpKey, keyLength, fState);

fx = fy = 0;

for (j = 0; j < 32; ++j)

{

test[j] = rc4EncryptByte(fState, &fx, &fy, test[j]);

}

｝

PDF document (portable document format), general clusters, can be used in UNIX, Apple, Windows, Linux platform for reading, ADOBE company developed the Acrobat PDF Reader is very closer with traditional reading books, it makes reading very cheerful. In recent years, PDF is known by more and more people, more and more people through the PDF to paste information on the Internet, a lot of eBooks are also the PDF format, in fact, PDF document has already become the industry standard. In May 2005, PDF has become permanently the document saving information standard, this will be more will accelerate the development of the PDF and dissemination, the application of PDF will become more and more widely. If you want to know more about PDF information, please use the search engines:

 

 Tips: when you get the pdf open password, you may need a PDF editor mac and PDF to ePub converter to convert PDF to others format.

We open PDF at ordinary times, sometimes found there a lock mark at the bottom left corner of the status bar READER, then it means that the PDF is encrypted, you open the File-> Document properties, and then turn to the Security properties page, we may find the following content:

We can see from above, including printing, document changes, copying the content of the document are all limited, How to implement if limiting the different jurisdiction. Documents need to be printed or other use is limited jurisdiction need to enter a Permission Password, however, how does PDF viewer (such as PDF Reader) know the input PASSWORD is correct or not? how to realize the authority after let go when Inputting the correct key? PDF has the two group password based encrypted password, in addition to the above mentioned permissions password, another is the open password, it will pop up a dialog box that enables you to enter the correct password when you open a protected document with PDF reader. if right, so you can open a document, or failure. Then how does this password realize? I will give the answer in the late article.

If the friends may be more familiar to PDF , may have used some remove PDF software, such as the PDF Password remover, etc, which normally only remove permissions Password, but it still can't remove passwords for the PDF owned the open password. So why can only go to access the Password and can't remove the open Password? What’s the relation and differences between them, We will also analyze it.

Here is the guide on how to remove PDF password and open password by using decryption program.

1. 1.       (1) Launch PDF Password Remover, then choose the "Add Files..." button in the interface to add the PDF files and click "Start" button to remove password from PDF.

 

 (2) Specify an output folder for the exported PDF files

If you want to specify an output folder for the exported PDF files, please select Customize and click the "Open" button to specify a folder on your computer.

2.       How to create PDF password

Most of time, PDF Password is added in PDF Editor. If you have Adobe Acrobat, you could easily create PDF password. Click"Secure" button and select encrypt with password. In pop-up window of Password Security- Settings, you can set the open password and owner password. Besides of Adobe Acrobat, you can use other third- party software for creating PDF password too. And there are a great many online; you can look them up in Google.

 

We have introduced the PDF encryption algorithm, we will turn to a series of application, how to encrypt PDF files by encryption program, decryption. I'll properly provide some simple source code, let us together to discuss and improve.

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