U3D or PRC, and various iges file format pdf data formats. Adobe Systems made the PDF specification available free of charge in 1993. ISO 32000-2 does not include any proprietary technologies as normative references. A structured storage system to bundle these elements and any associated content into a single file, with data compression where appropriate.
Any files, graphics, or fonts to which the document refers also are collected. Then, everything is compressed to a single file. A PDF file is a 7-bit ASCII file, except for certain elements that may have binary content. Indirect objects are numbered with an object number and a generation number and defined between the obj and endobj keywords. An index table, also called the cross-reference table and marked with the xref keyword, follows the main body and gives the byte offset of each indirect object from the start of the file.
At the end of a PDF file is a trailer introduced with the trailer keyword. Non-linear PDF files consume less disk space than their linear counterparts, though they are slower to access because portions of the data required to assemble pages of the document are scattered throughout the PDF file. PDF graphics use a device-independent Cartesian coordinate system to describe the surface of a page. Paths are usually composed of lines and cubic Bézier curves, but can also be constructed from the outlines of text.
PDF supports several types of patterns. The simplest is the tiling pattern in which a piece of artwork is specified to be drawn repeatedly. This may be a colored tiling pattern, with the colors specified in the pattern object, or an uncolored tiling pattern, which defers color specification to the time the pattern is drawn. 3 there is also a shading pattern, which draws continuously varying colors. The dictionary describes properties of the image, and the stream contains the image data. Less commonly, a raster image may be embedded directly in a page description as an inline image. Images are typically filtered for compression purposes.
LZW compression: Predictor 2 from the TIFF 6. JBIG2 standard, introduced in PDF 1. JPXDecode a lossy or lossless filter based on the JPEG 2000 standard, introduced in PDF 1. Normally all image content in a PDF is embedded in the file. But PDF allows image data to be stored in external files by the use of external streams or Alternate Images.
Text in PDF is represented by text elements in page content streams. A text element specifies that characters should be drawn at certain positions. The characters are specified using the encoding of a selected font resource. A font object in PDF is a description of a digital typeface. It may either describe the characteristics of a typeface, or it may include an embedded font file. The latter case is called an embedded font while the former is called an unembedded font. These fonts are sometimes called the base fourteen fonts.