PDF (Portable Document Format Structured Document Format) Adobe Corporation (http: // www.Adobe.com) the development of an electronic document format, which can be text, font, format, color, graphic images, hypertext links, sound, dynamic graphics and other information in a paper package. PDF page description language from the PS (PostScript) evolved with the PS is almost the same as the page description and a description of a similar method. However, PS is different, PDF In addition to the complexity of the layout description, but also has interactive features (such as hyperlinks, interactive forms, etc.), page Simulation random access and description of characteristics of the font. Therefore, PDF is not only suitable for printing and publishing, but also suitable for electronic publishing. PDF and electronic publishing in the dominant compared to the HTML language has its own distinct advantage. HTML can not describe the layout, and PDF to describe the layout attractive; HTML page that often appear inconsistent information (such as the different platforms, different browsers, different sizes of the browser window to see the same web page showing a different way), and In the PDF of this issue does not exist; HTML page in the need to save separate images, and PDF documents can be saved in one step. PS and PDF is not only the advantages of both HTML, but also to overcome their shortcomings, in order to achieve a paper published in print and electronic unity. After publishing the content to generate PDF documents, you can at the same time in the delivery of the printing, distribution network.
1 PDF of the structure
PDF document is the object through a series of sequences to construct, PDF objects, including a direct object (Direct Object) and indirect object (Indirect Object). Indirect object is a logo of the PDF object, direct object usually Boolean (Boolean), numeric (Number), the string type (String), type the name of (Name), an array of type (Array), a typical character (Dictionary) , empty object (Null), the object stream (Stream) and other basic types. A PDF document contains one or more pages, and each page can contain documents, graphics and images. A typical PDF file contains four parts, which are: the first document, document main body, document cross-reference table and the end. File Header (Header) is located in the first line of PDF document, it shows that the use of the current paper version of PDF specification; document body (Body), including a document constitutes a sequence of indirect objects, these objects represent the various components of the document, such as fonts, page and image and so the tree.
Cross-reference table (Cross-reference Table) is the indirect object in order to be able to set up random access to the target address of an indirect index table, it is given all the current paper addresses the use of imported objects, that is, byte offset, random access to different systems of the object; file tail (Trailer) contains cross-reference table in which the starting address and the total number of objects, documents Catalog (directory) as well as its object the object of encryption, such as security information, according to documents provided by the end of PDF application information can be found cross-reference table and the entire PDF document directory object, and thus control the entire PDF document.