4. Logical structure of PDF documents
As a structured file format, a PDF document by a number known as the "target" of the modules. Each object has the number and grade, so these objects can be the object of the north quoted other. In accordance with the order of these objects do not need to appear in the PDF file inside, there can be any order, such as a PDF document 3, p. 3 can appear in the first page of the past, the object appears only in accordance with the order is to increase the benefits of the readability of documents, if you will not use a text editor to read the PDF structure, so no need for concern. It is because between the pages and pages of irrelevant, you can page to the PDF file to a random visit.
File tail (Trail), that the object of its root object, and note the location of cross-reference table, cross-reference table of the query object can be directory (Catalog). This directory is the root of the target PDF document, PDF document contains an outline (outline) and page group objects (pages) cited. Outline PDF document object refers to the bookmark tree; page group objects (pages) contains a few pages of the document, each page object (page) number of objects.
Under a PDF document has shown the relationship between the level of:

Figure 2

page (page) object as a PDF of the most important objects, including how to display the page information, such as the use of fonts, the content (text, pictures, etc.), the size of the page. Of course there can also be a subset of other object. The information contained in the page is included in a group called the flow (stream) of the object, the length of this flow (bytes) must be given direct or point to another object. The following chart:

Figure 3