If you want users to download an XPS document from a server (e.g., from a website), you need to enable the server to do this by registering the MIME types and file extensions.
The following steps pertain to a server running Microsoft Internet Information Services (IIS). You should provide this information to the individual(s) responsible for software on your company's server. Exact steps may vary depending on the operating system.
How to register a MIME type and file extensions for XPS output
Double-click Add or Remove Programs.
The Add or Remove Programs window opens.
Click Add/Remove Windows Components.
The Windows Components Wizard opens.
In the Control Panel, double-click Administrative Tools.
The Administrative Tools dialog opens.
Double-click Internet Information Services.
The Internet Information Services dialog opens.
Select Properties.
The Default Web Site Properties dialog opens.
In the MIME Map section, click File Types or MIME Types.
Note: For more information see this article: http://msdn.microsoft.com/en-us/library/ms752346.aspx.