PDF Password Encryption

PDF (Portable Document Format), commonly used in file formats, available in Unix,

Apple, Windows,linux on any platform, the Adobe-developed Acrobat and PDF reader is very close to reading PDF files and reading traditional books, which makes reading very enjoyable. In recent years, PD

F is recognized by more and more people, more and more people publish information via PDF on the Internet, many e-books are in PDF format, in fact, PDF has already become the industry's document standard. May 2005, pdf into

In order to keep the document standard of information permanently, this will accelerate the development and spread of PDF, and the application of PDF will become more and more extensive. If you want to know more about PDFs, use the search engine:

When we open the PDF, sometimes we will find the reader status bar in the lower left corner will have a lock tag, then means that the PDF is encrypted, you open file->document properties, and then go to the Security property page, We may find the following:

As can be seen from the above, including printing, changes to the document, copying the contents of the document are limited, and how to limit the different permissions are implemented. When a document needs to be printed or other restricted permissions to enter a permission Passwrod, how does a PDF viewer (such as PDF Reader) know if the input is password correct or not? After you enter the correct key, how do you implement permission? PDF password based encryption has two sets of passwords, in addition to the password mentioned above, there is another open password, that is, when you open the password-protected document with a PDF reader, a dialog box pops up to allow you to enter the password and, if it is correct, you can open the document or fail. So how does this password work in the PDF? What is the technical difference between opening a password and a permission password? I will give the answer in the following document.

If you are familiar with the PDF friends may have used some software to remove the PDF password, such as the more popular PDF Password remover, and so on, they generally can only remove the PDF permission password, for the open password of the PDF or can not be removed, So why do you have to go to the right password instead of opening the password? What is the relationship and difference between the two? We will also conduct a comparative analysis.

In addition to password based document encryption and permission control, PDF can also be public key encryption and signature, then how to achieve it. You will also see in the following articles.

After introducing the encryption algorithm of PDF, we will turn to a series of applications, how to encrypt and decrypt the PDF file through the program. Appropriately I will provide you with some simple source code, let us all discuss and improve.

Another: In addition to the PDF encryption algorithm, I will introduce several to Adobe Acrobat and Adobe PDF Reader's programming introduction, if which friends have not contacted the relevant knowledge, then I hope I can give these friends a primer, can give everyone a starting point, A more comprehensive introduction to the current programming techniques for PDFs.

For those who are already in the development of the PDF, I also hope that you can make a lot of your own views and ideas, but also hope that you can bring their experience to you. Let's make progress together.