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PDF Spec Annex E
Part of: PDF-Spec-Annexes
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- Third class . Names that may be used only in PDF files that other third parties will never see because they can conflict with third-class names defined by others. Third-class names shall all begin with a specific prefix reserved for private extensions. This prefix, which is XX, shall be used as the first characters in the names of all private data added by the developer. It is not necessary to contact ISO to register third-class names.
New keys for the document information dictionary (see 14.3.3, "Document Information Dictionary") or a thread information dictionary (in the I entry of a thread dictionary; see Section 12.4.3, 'Articles') shall not be registered.
More information about developer prefixes, handlers and extensions to ISO 32000-1 can be obtained at http:// www.aiim.org/ISO32000Registry.
Linearization of PDF is an optional feature available beginning in PDF 1.2 that enables efficient incremental access of the file in a network environment. A conforming reader that does not support this optional feature can still successfully process linearized files although not as efficiently. Enhanced conforming readers can recognize that a PDF file has been linearized and may take advantage of that organization (as well as added hint information) to enhance viewing performance.
The primary goal for a linearized PDF file is to achieve the following behaviour for documents of arbitrary size and so that the total number of pages in the document should have little or no effect on the user-perceived performance of viewing any particular page:
- When a document is opened, display the first page as quickly as possible. The first page to be viewed may be an arbitrary page of the document, not necessarily page 0 (though opening at page 0 is most common).
- When the user requests another page of an open document (for example, by going to the next page or by following a link to an arbitrary page), display that page as quickly as possible.
- When data for a page is delivered over a slow channel, display the page incrementally as it arrives. To the extent possible, display the most useful data first.
- Permit user interaction, such as following a link, to be performed even before the entire page has been received and displayed.
NOTE A linearized PDF is optimized for viewing of read-only PDF documents. A linearized PDF should be generated once and read many times.
Incremental update shall still be permitted, but the resulting PDF is no longer linearized and subsequently shall be treated as ordinary PDF. Linearizing it again may require reprocessing the entire file; see G.7, "Accessing an Updated File" for details.
Linearized PDF requires two additions to the PDF specification:
- Rules for the ordering of objects in the PDF file
- Additional optional data structures, called hint tables , that enable efficient navigation within the document
Both of these additions are relatively simple to describe; however, using them effectively requires a deeper understanding of their purpose. Consequently, this annex goes considerably beyond a simple specification of these PDF extensions to include background, motivation, and strategies.
- F.2, "Background and Assumptions," provides background information about the properties of the Web that are relevant to the design of Linearized PDF.
- F.3, "Linearized PDF Document Structure," specifies the file format and object-ordering requirements of Linearized PDF.
- F.4, "Hint Tables," specifies the detailed representation of the hint tables.
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