Vista - How to use document viewer?

Does anyone know how to load a document in the document viewer?

First you have to have the correct kind of document, if you are trying to
load an XPS document, you can use the Packaging apis to load the file, get
access to the FixedDocumentSequence, and set it on the DocumentViewer:

DocumentViewer viewer = new DocumentViewer();
XpsDocument doc = new XpsDocument(filename, FileAccess.Read);
viewer.Document = doc.GetFixedDocumentSequence();

If you are trying to directly load a FixedDocument or FixedDocumentSequence
that is outside your assembly (e.g. not compiled into your app) you can use:

IDocumentPaginatorSource doc = (IDocumentPaginatorSource)
XamlReader.Load(Stream);

This will parse the stream and create the corresponding WPF object which you
can set on the viewer. Note: this approach can be a bit trickier because the
relative paths in the document definition might be off depending on the
document's location relative to the executable.

Finally if you are trying to load a FixedDocument or FixedDocumentSequence
directly AND it has been compiled into your app, you can use:

IDocumentPaginatorSource doc = (IDocumentPaginatorSource)
XamlReader.Load(Application.GetResourceStream(fileUri).Stream);

Hope this helps.
-Derek
http://blogs.msdn.com/mehlhorn/default.aspx