Indirect objects are numbered with an object number and a generation number and defined between the This design allows for efficient random access to the objects in the file, and also allows for small changes to be made without rewriting the entire file (incremental update).
Beginning with PDF version 1.5, indirect objects may also be located in special streams known as object streams.
PDF files may be optimized using Adobe Acrobat software or QPDF.
The Portable Document Format (PDF) (redundantly: PDF format) is a file format developed by Adobe in the 1990s to present documents, including text formatting and images, in a manner independent of application software, hardware, and operating systems.
Based on the Post Script language, each PDF file encapsulates a complete description of a fixed-layout flat document, including the text, fonts, vector graphics, raster images and other information needed to display it.
Adobe Systems made the PDF specification available free of charge in 1993.
In the early years PDF was popular mainly in desktop publishing workflows, and competed with a variety of formats such as Dj Vu, Envoy, Common Ground Digital Paper, Farallon Replica and even Adobe's own Post Script format.
Any files, graphics, or fonts to which the document refers also are collected. Therefore, the entire Post Script world (fonts, layout, measurements) remains intact.
As a document format, PDF has several advantages over Post Script: ). Objects may be either direct (embedded in another object) or indirect.PDF 1.7, the sixth edition of the PDF specification that became ISO 32000-1, includes some proprietary technologies defined only by Adobe, such as Adobe XML Forms Architecture (XFA) and Java Script extension for Acrobat, which are referenced by ISO 32000-1 as normative and indispensable for the full implementation of the ISO 32000-1 specification.These proprietary technologies are not standardized and their specification is published only on Adobe’s website.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.Linear PDF files (also called "optimized" or "web optimized" PDF files) are constructed in a manner that enables them to be read in a Web browser plugin without waiting for the entire file to download, since they are written to disk in a linear (as in page order) fashion.There are seven types of shading pattern of which the simplest are the axial shade (Type 2) and radial shade (Type 3).