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PDF20 Spec 07 General
Part of: PDF20-Spec-07-Syntax
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7 Syntax 7.1
General
This clause covers everything about the syntax of a PDF file at the object, file, and document level. It sets the stage for subsequent clauses, which describe how the contents of a PDF file are interpreted as page descriptions, interactive navigational aids, and application-level logical structure. PDF file syntax is best understood by considering it as four parts, as shown in "Figure 1 — PDF file components": •
Objects. A PDF file is a data structure composed from a small set of basic types of data objects. Subclause 7.2, "Lexical conventions" describes the character set used to write objects and other syntactic elements. Subclause 7.3, "Objects" describes the syntax and essential properties of the objects. Subclause 7.3.8, "Stream objects" provides complete details of the most complex data type, the stream object. Subclause 7.4, "Filters" introduces stream filters primarily used to make PDF files smaller by applying compression technology to stream data.
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File structure. The PDF file structure determines how objects are stored in a PDF file, how they are accessed, and how they are updated. This structure is independent of the semantics of the objects. Subclause 7.5, "File structure" describes the file structure. Subclause 7.6, "Encryption" describes a file-level mechanism for protecting a document’s content from unauthorised access.
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Document structure. The PDF file structure specifies how the basic object types are used to represent components of a PDF file: pages, fonts, annotations, and so forth. Subclause 7.7, "Document structure" describes the overall document structure; later clauses address the detailed semantics of the components.
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Content streams. A PDF content stream contains a sequence of instructions describing the appearance of a page or other graphical entity. These instructions, while also represented as objects, are conceptually distinct from the objects that represent the document structure and are described separately. Subclause 7.8, "Content streams and resources" discusses PDF content streams and their associated resources.
Figure 1 — PDF file components In addition, this clause describes some data structures, built from basic objects, that are so widely used that they can almost be considered basic object types in their own right. These objects are covered in: 7.9, "Common data structures"; 7.10, "Functions"; and 7.11, "File specifications". Subclause 7.12, "Extensions dictionary" describes a dictionary used to identify developer-defined extensions to this document that are used in the file.
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© ISO 2020 – All rights reserved
ISO 32000-2:2020(E)
NOTE
Variants of PDF’s object and file syntax are also used as the basis for other file formats. These include the Forms Data Format (FDF), described in 12.7.8, "Forms data format", and the Portable Job Ticket Format (PJTF), described in Adobe Technical Note #5620, Portable Job Ticket Format.
Annex H, "Example PDF file" presents several examples showing the structure of PDF files.
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