PDF is currently very popular both offline and online. When this file extension was first invented , in 1990 , the Internet was only childish. At that time this file format was widely used especially offline. PDFs were used for offline document printing , posters , or any document printing from the desktop. However, in today's world of PDF, there are so many types of things that can be stored in a PDF, not so much in the beginning. There was a problem with the PDF , the big document files were too big and too slow , the files would open and the system would read twelve times.