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PDF File

Portable Document Format (PDF) was introduced by Adobe in 1993 as a document format independent of the device hardware, software and operating system. Initially after release PDF was popular for a pre-print document exchange in publishing business competing or complementing Postscript file format. In 2008 Adobe opened specification for PDF and made it available for free to the development community. This led to PDF becoming widely successful as a document exchange format on the internet and it is currently the most popular document format with almost 80% of the market share.

PDF file format is based on Carousel Object Structure (COS) which is a text-based format for representing structured hierarchical data. COS is a format which in its concepts is similar to XML and JSON but also has support for data streams, indirect objects, references and comments. Each PDF file consists of multiple objects (sometimes referred to as COS objects). Objects in PDF could have one of the following types: null, Boolean, integer, real, stream, name, string, array, dictionary. For more details about PDF internal structure refer to PDF specification.

Besides storing textual document information PDF supports embedding of raster images, rich vector graphics, coordinate system with transformation matrix, embedded fonts, and transparency. Recently introduced AcroForms PDF format extension allows creation of forms with interactive elements such as form fields, annotations, rich media, 3D and video. Recent versions of PDF format support encryption, password protection and digital signature support which makes it possible to use PDF for advanced document workflow applications.

PDF files could be opened by Adobe Acrobat Reader, a free software which is available for download from Adobe Acrobat Reader is available for Microsoft Windows, Mac OS and Android operating system. On iOS devices PDF files are supported by the operating system natively.

Multiple software packages support export to PDF file format. This includes Microsoft Office, Apple Office, CorelDraw, Adobe Illustrator and many others. PDF files could be natively created in Adobe Acrobat Software which is paid software package from Adobe.