2.4. PDF and the PostScript Language

The PDF operators for setting the graphics state and painting graphics objects are similar to the corresponding operators in the PostScript language. Unlike PostScript, however, PDF is not a full-scale programming language; it trades reduced flexibility for improved efficiency and predictability. PDF therefore differs from PostScript in the following significant ways:

• PDF enforces a strictly defined file structure that allows an application to access parts of a document in arbitrary order.

• To simplify the processing of content streams, PDF does not include common programming language features such as procedures, variables, and control constructs.

• PDF files contain information such as font metrics to ensure viewing fidelity.

• A PDF file may contain additional information that is not directly connected with the imaging model, such as hypertext links for interactive viewing and logical structure information for document interchange.