Portable Document Format
The Portable Document Format (PDF) is a file format for storing documents on a computer. Adobe created it in 1993 to make it easier to exchange documents. PDF is often used to make documents print-ready. PDF documents can have stylised text and images in them.
The document is stored in such a way that the content does not change the way it looks on different screens, computers and printers as can happen with other file formats.
PDF reader software is required to read PDF documents. make more informantion on the pdf