Portable Document Format (PDF) is a type of file format developed by Adobe Systems. It was first introduced in 1993 and is capable of capturing content and formatting information from any document; irrespective of the hardware and operating system platform. It was initially a proprietary file format; however PDF has been available as an open format from 2008 and adheres to the ISO/IEC 3200-1:2008 standard. The current PDF version is 1.7 Extension Level 3.

PDF documents require PDF viewing software such as Adobe Reader, Xpdf, Foxit Reader, Evince and so on. Most operating systems and software applications have built-in functionality for creating and printing PDF files. Operating systems such as Mac OS X, Microsoft Windows and certain versions of Linux support the printing and creation of PDF documents. Software applications such as WordPerfect, DocBook, Ghostscript and Adobe Acrobat are capable of printing and creating PDF documents.

PDF file structure

A PDF document comprises of eight types of objects. They are as follows:

  • Numbers
  • Strings
  • Boolean
  • Arrays
  • Names
  • Streams
  • Null
  • Dictionaries

The common structure of a PDF file comprises of the following code modules: header, body, xref table and trailer. The header consists of one line of code that categorizes the version of PDF. The body holds all the object data such as fonts, words, images and so on. The xref table has all the indicators to the objects in the file. It specifies the number of objects in the table, object point of origin and its byte length.

Key PDF features

The most important feature of the PDF file format is that it can be viewed and printed on literally any platform inclusive of the most popular ones such as Microsoft Windows and Mac OS, and even Unix and mobile platforms. PDF offers great extensibility as well. There are a large number of software vendors that produce plug-in, creation and support tools. PDF documents protect the original file information inclusive of text, images, drawing, original graphics, 3D and other elements. PDF files can be encrypted or authenticated via digital signature. PDF document creators can set a password for opening the file. Restrictions can also be imposed even after the document is open. PDF is perhaps the most popular document format in use today. There are more than 250 million PDF documents present on the internet, which is a clear indicator of its wide application and use.