XPS (XML Paper Specifications) is a free electronic paper format developed by Microsoft. It was developed to be an alternative to the widely popular PDF format. In most cases, 3rd party scanning tools in Windows will save documents in XPS format
Windows 7 & Windows Vista already have Microsoft’s XPS Viewer installed by default. But if you are using Windows XP then you need Microsoft XML Paper Specification Essentials Pack to open XPS Files.
The Microsoft XML Paper Specification Essentials Pack, Version 1.1 (XPS Essentials Pack) contains components that enable you to view, generate and index XPS Documents.