What is PDF?

Portable Document Format (PDF) is a file format proprietary to Adobe Systems Inc. It is used in 1993 for document exchange first time. It represented two-dimensional documents in a device independent and resolution independent fixed-layout document format. Later, it extended to Acrobat 3D and embedded 3D documents.

PDF is officially declared as an open standard on July 1, 2008. It becomes now ISO 32000 (International Organization for Standardization). According to one estimate, there are more than one billion files are in existence today.

PDF is a digital form of document to view, print, and preserve content and visual appearance, independent of the environment (Microsoft Windows, Apple Macintosh, Unix and Linux and manyy mobile platforms). Its allows users to:

preserve document fidelity independent of device or platform
merge content from diverse sources
edit documents collaboratively in multiple platforms
apply digital signatures for authenticity
set security and permissions to preserve control over content
allow content accessibility for people with disabilities
extract and reuse of content in other file formats, and
collect and integrate data for business systems

PDF file is set of objects such as numbers and strings. PDF vector images are usually composed of Bézier curves. PDF raster images are represented by dictionaries and streams. Images are compressed using filters:

ASCII85: puts the stream into 7-bit ASCII
ASCIIHex: same as ASCII85 but less compact
Flate: is based on Deflate or Zip algorithm
LZW: is based on LZW Compression
RLE: is a compression method using Run Length Encoding algorithm
DCT: is based on the JPEG standard
CCITTFax: is based on CCITT fax compression standard
JBIG2: is based on JBIG2 standard, introduced in PDF 1.4
JPX: is based on the JPEG2000 standard, introduced in PDF 1.5

Adobe has made many improvements from the PDF version 1.0 released in June 1993.


PDF Version	Release Year	PDF Reader	Features
1.0	1993	Acrobat Reader 1	First release with basic features
1.1	1994	Acrobat Reader 2	Colors, links and passwords
1.2	1996	Acrobat Reader 3	Unicode, multimedia, and mouse events
1.3	2000	Acrobat Reader 4	Digital signatures, ICC color and JavaScript actions
1.4	2001	Acrobat Reader 5	JBIG2, transparency, and OCR text layer
1.5	2003	Adobe Reader 6	JPEG2000, linked multimedia, object streams, and cross reference streams
1.6	2004	Adobe Reader 7	Embedded multimedia and XML forms
1.7	2006	Adobe Reader 8	Digital signatures, ICC color and JavaScript actions
1.7 Extension	2008	Adobe Reader 9	256-bit AES encryption
1.8	2010	Adobe Reader X	Commenting, rich multimedia, international standards conformance, software rollouts

Adobe Reader is a free software distributed by Adobe Inc. It can be downloaded by clicking the button:

There are many other software firms developed PDF readers with different features and file sizes. ISO 32000 protects the PDF integrity and longevity. PDF continues to be used as one of the most trusted file formats.

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