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Adobe PDF Overview

April 22nd, 2008

adobe-pdf-logo.jpgIn the Internet marketing world, PDF files are commonly used for packaging and transmitting digital information products such as ebooks. This article by Dario Borghino provides a brief summary of the advantages and disadvantages of this particular file format.

The Portable Document Format (PDF) is a widespread file format developed by Adobe Systems in 1993 whose main feature is the independence over a particular hardware, software, or operating system. Its format specifications are released by Adobe under the Public Domain, effectively making it a convenient choice for cross-platform document exchange.

This format can include formatted text, images, bitmap images and even two-dimensional vector graphics, while further possibilities exist to embed 3D graphics and documents. A PDF file usually has a very distinctive, elegant look, and is therefore often the preferred file format for official documents, press releases, and research papers that had previously been written and compiled using the (La)Tex formatting language.

The file structure of a PDF file is object-based. There are several kinds of objects, which include:

  1. Boolean variables, which can be assigned either the value ‘true’ or ‘false’;
  2. Arrays, a set of different objects which are often ordered;
  3. Maps, which are similar to databases in which a list of key values (titles) maps other objects (contents);
  4. Data Streams, containing bulks of data;
  5. Names, numbers, etc.

The PDF format lays its foundations on the PostScript page description language in order to generate document layouts and manage complex graphics issues. However, the main advantages of PDF over PostScript are the possibility of including transparency effects and, in a more technical context, the fact that unlike PostScript, PDF does not adopt a so-called ‘imperative programming style’ making use of global variables that are deprecated because of efficiency issues. In order to determine the appearance of a given page, it is necessary to process all the previous ones. To some extent, we may say that PostScript is slowly becoming a subset of the Portable Document Format family.

The impossibility of editing a PDF file is often seen as the main drawback of this format. Software exists to apply minor modifications such as removing an entire page or inserting a new one. However, in order to obtain a greater level of flexibility you would have to own the original document from which the PDF was created, as modifications such as changing the font size, layout or editing the text body are normally not permitted directly on the PDF file. However, other publishers see this as an extremely useful feature when they have to make sure their documents won’t get manipulated and redistributed by competitors or third parties.

Many computer programs, and most notably the OpenOffice open source, cross-platform software suite developed by Sun Microsystems, embed a PDF converter which will transform many of the most common rich-formatted file extensions (be it DOC, RTF or ODT) into a PDF unmodifiable file, but not vice versa. Tools exist on Linux and Apple platforms to convert PDF into plain .txt text files (pdf2txt) in a straightforward way, but tools attempting more complex conversions (such as PDF to DOC) will often yield unsatisfactory results in the page layout and will usually require further manual intervention.

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