If you need to use XpsDocument class in your WPF project, you must add reference to System.Windows.Xps.Packaging namespace. However, the assembly in which this namespace is defined is not a part of a WPF application by default. It is defined in the ReachFramework.
To add reference to ReachFramework, you right click on Add
Reference on the project name in Solution Explorer. On the .NET Framework,
select ReachFramework and other assemblies from the list and click OK button.
Figure 1 shows ReachFramework in Add Reference dialog.
![reachframeworkimg.jpg]()
Figure 1
After adding this reference, you should be able to use XpsDocument in your WPF applications.