ID number of the PDF file

ID number of the PDF file

1 ID cardEach adult has an ID card with a lot of information, including our name, gender, nationality, date of birth, and ID card number. and each person's ID card number is different. The information on these ID cards, including the province ID card, enters the information library. In some cases, we often enter our ID card numbers, such as when starting a bank account. Once you have this number, the bank can obtain your other basic information, because your ID card number is unique and other information on the ID card is not unique, there are many people with the same name, and there are more people with the same birth date. Similarly, there are goods tags in supermarkets. Each tag has only one barcode and corresponding number, but this barcode has a lot of corresponding information, therefore, after reading and scanning, you can get the corresponding goods name, factory date, price, and other information. For goods, the bar code is its ID card number, which facilitates and accelerates the sales and management of goods. 2. ID number of the PDF fileEach PDF file has a unique string corresponding to the file. We can regard it as the ID number of the PDF file, and its string is saved in the trailer Dictionary of the file. Open a PDF file in the text editor and you can see: </size433/root 1 0 r/INFO 3 0 r/ID [<2c12621cbd44224ca14c29823a6b31f4> <strong>]> the red part is the file ID. ID is an array with two elements, both of which are 32 bytes in length and have the same content. The first element remains unchanged, and the second element changes with the revision of the PDF file. I modified the file in Acrobat. The trailer dictionary is changed to the following: </size433/root 1 0 r/INFO 3 0 r/ID [<strong> <bc67f3302da-184da5cce275d6bd836d>]> we will find that the second element of the ID array has changed, this PDF file has been modified after it is created. 3. How to obtain the ID number of a PDF fileHow is this ID generated? The PDF specification is not limited. If you want to generate a PDF file, you can define your own method to generate this ID. Of course, you must ensure the uniqueness of this ID. Therefore, this ID is generally a hash sequence generated by file content, file generation or modification date, or even computer hardware information. 4. Functions of PDF File ID card numbersThe ID in PDF is particularly useful for the processing process of some documents. to manage a large number of files, we must create a file information table and set a unique ID for each file, this ID is generally a serial number. In this way, the system coupling is very large and it is easy to cause File Duplication and space waste. For example, we have two such systems, each of which maintains a database independently. We may enter some identical files in these two systems, however, their idnumbers are different. Therefore, if you want to merge these two databases (nor merge them), it will inevitably cause a great waste of resources. Generally, our document system has a server and a client browser. If the Id carried by the PDF file is used as a unique identifier, it is unnecessary to transmit additional information, the ghost browser can use the ID in the PDF file to interact with the server and manage the server, greatly facilitating the document processing process.