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