Format
The XPS document format consists of structured XML markup that defines the layout of a document and the visual appearance of each page, along with rendering rules for distributing, archiving, rendering, processing and printing the documents. Notably, the markup language for XPS is a subset of XAML, allowing it to incorporate vector-graphic elements in documents, using XAML to mark up the Windows Presentation Foundation (WPF) primitives. The elements used are described in terms of paths and other geometrical primitives.
An XPS file is, in fact, a Unicoded ZIP archive using the Open Packaging Conventions, containing the files which make up the document. These include an XML markup file for each page, text, embedded fonts, raster images, 2D vector graphics, as well as the digital rights management information. The contents of an XPS file can be examined simply by opening it in an application which supports ZIP files.
Read more about this topic: Open XML Paper Specification