PDF password encryption

PDF (Portable Document Format), common document format, can be in UNIX,

Reading on any platform of apple, windows, and Linux is very similar to reading PDF files and reading traditional books through acrobat and PDF Reader developed by Adobe. In recent years, PD

F has been recognized by more and more people, and more people publish information on the Internet through pdf. Many e-books are also in pdf format. In fact, PDF has already become a document standard in the industry. May 2005, PDF

In order to permanently Save the document standards of information, this will accelerate the development and dissemination of PDF, and the application of PDF will become more and more extensive. If you want more information about PDF, please use the search engine :)

 

 

 

When we open a PDF file, we sometimes find a lock icon in the lower left corner of the reader status bar.
In this case, the PDF file is encrypted. Open File> document properties and go to the Security Attribute page. We may find the following content:

As we can see from the above, printing, modifying documents, copying documents are all restricted. How can different permissions be restricted? When a document needs to be printed or other restricted permissions, you need to enter a permission passwrod. How does the PDF Viewer (such as PDF Reader) know whether the entered password is correct? After entering the correct key, how can I open the permission? PDF password-based encryption has two sets of passwords. In addition to the permission password mentioned above, another one is to open the password, that is, when you open the password-protected document with a pdf reader, A dialog box will pop up asking you to enter the password. If the password is correct, you can open the document. Otherwise, the document fails. How is this password implemented in PDF? What are the technical differences between a password and a permission? In this case, I will give answers one by one in subsequent documents.

If you are familiar with PDF, you may have used some software to remove the PDF permission password, such as the popular pdf password remover, they can only remove the PDF permission password, PDF files with a password cannot be removed. Why can't I open a password instead of a permission password? What is the relationship and difference between the two? We will also conduct comparative analysis.

In addition to password-based document encryption and permission control, PDF can also encrypt and sign public keys. How can this problem be achieved? You will also see it in subsequent articles.

After introducing the PDF encryption algorithm, we will turn to a series of applications, how to encrypt and decrypt PDF files through programs. As appropriate, I will provide you with some simple source code for discussion and improvement.

 

 

 

In addition to the PDF encryption algorithm, I will introduce several programming introductions for Adobe Acrobat and Adobe PDF reader. If any of you have never touched on this knowledge, so I hope I can give these friends an introduction and give you a starting point to give a comprehensive introduction to the PDF programming technology.

For experts who are already developing PDF files, I hope you can give more comments and opinions and bring your experience to everyone. Let us make progress together.