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                                    CHAPTER 1


                             1   Introduction

    The Adobe Portable Document Format (PDF) is the native file format of the
    Adobe® Acrobat® family of products. The goal of these products is to enable users
    to exchange and view electronic documents easily and reliably, independently of
    the environment in which they were created. PDF relies on the same imaging
    model as the PostScript® page description language to describe text and graphics
    in a device-independent and resolution-independent manner. To improve perfor-
    mance for interactive viewing, PDF defines a more structured format than that
    used by most PostScript language programs. PDF also includes objects, such as
    annotations and hypertext links, that are not part of the page itself but are useful
    for interactive viewing and document interchange.


1.1 About This Book

    This book provides a description of the PDF file format and is intended primarily
    for developers of PDF producer applications that create PDF files directly. It also
    contains enough information to allow developers to write PDF consumer applica-
    tions that read existing PDF files and interpret or modify their contents.

    Although the PDF Reference is independent of any particular software implemen-
    tation, some PDF features are best explained by describing the way they are pro-
    cessed by a typical application program. In such cases, this book uses the Acrobat
    family of PDF viewer applications as its model. (The prototypical viewer is the
    fully capable Acrobat product, not the limited Adobe Reader® product.) Appendix
    C discusses some implementation limits in the Acrobat viewer applications, even
    though these limits are not part of the file format itself. Appendix H provides
    compatibility and implementation notes that describe how Acrobat viewers be-
    have when they encounter newer features they do not understand and specify ar-
    eas in which the Acrobat products diverge from the specification presented in



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