The PDF Era
PDF or Portable Document Format is the de facto standard in digital publishing and archival. The format evolved from PostScript, and hence continues using most of its features. A PDF document is stored in 2-D using technology and techniques that make it portable with respect to hardware, software and operating systems. This is a key factor for global acceptance of PDF files as a standard for desktop publishing. The PDF file format has entered the public domain as an open standard since 2008. This allows developers to create their own PDF reading and writing software with their own implementation of features. This is achieved using SDKs or Standard Development Kits available for integrating the functionality of PDF file format within existing software.
PDF Technologies and Techniques
The PDF file format primarily comprises of a subset of the PostScript programming language in order to generate graphics and layout. It also has a system of embedding and replacing fonts within the PDF file itself. Another technology used in PDF file format is a structured storage system for all the matter that needs to be embedded within the PDF file, including the functionality to compress the components of the PDF. The images within a PDF can either be in the raster or vector format. A vector image is composed of 2-D paths as their minimum modifiable part, whereas raster images can be modified pixel-by-pixel. It is better to embed vector images in PDFs to decrease their size.
The other important features provided within PDF files are security and form filling. Form filling allows forms within PDF files to be filled interactively by the user. The concerns about security of such an embedded functionality are countered by the complex security mechanisms in PDFs. PDFs allow the file to be encrypted using 40- and 128-bit RC4 and MD5 algorithms. Third party encryption algorithms can also be defined in a PDF. Digital Rights Management can be implemented by limiting the copying, editing or printing of PDF files. However, this can be overcome using OCR conversion. Finally, servers can place a time restriction on offline PDF viewing.