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                                         26
CHAPTER 1                                                               Introduction



this book. Implementors of PDF producer and consumer applications can use
this information as guidance.

This edition of the PDF Reference describes version 1.7 of PDF. (See implementa-
tion note 1 in Appendix H.) Throughout the book, information specific to partic-
ular versions of PDF is marked with indicators such as (PDF 1.3) or (PDF 1.4).
Features so marked may be new or substantially redefined in that version. Fea-
tures designated (PDF 1.0) have generally been superseded in later versions; un-
less otherwise stated, features identified as specific to other versions are
understood to be available in later versions as well. (PDF consumer applications
designed for a specific PDF version generally ignore newer features they do not
recognize; implementation notes in Appendix H point out exceptions.)

Note: In this edition, the term consumer is generally used to refer to PDF processing
applications; viewer is reserved for applications that implement features that inter-
act with users. This distinction is not always clear, however, since non-interactive
applications may process objects in PDF documents (such as annotations) that rep-
resent interactive features.

The rest of the book is organized as follows:

• Chapter 2, “Overview,” briefly introduces the overall architecture of PDF and
  the design considerations behind it, compares it with the PostScript language,
  and describes the underlying imaging model that they share.
• Chapter 3, “Syntax,” presents the syntax of PDF at the object, file, and docu-
  ment level. It sets the stage for subsequent chapters, which describe how that
  information is interpreted as page descriptions, interactive navigational aids,
  and application-level logical structure.
• Chapter 4, “Graphics,” describes the graphics operators used to describe the
  appearance of pages in a PDF document.
• Chapter 5, “Text,” discusses PDF’s special facilities for presenting text in the
  form of character shapes, or glyphs, defined by fonts.
• Chapter 6, “Rendering,” considers how device-independent content descrip-
  tions are matched to the characteristics of a particular output device.
• Chapter 7, “Transparency,” discusses the operation of the transparent imaging
  model, introduced in PDF 1.4, in which objects can be painted with varying
  degrees of opacity, allowing the previous contents of the page to show through.

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