PrintDialog pd = new PrintDialog();
pd.PageRangeSelection = PageRangeSelection.AllPages;
pd.UserPageRangeEnabled = true;
Nullable<Boolean> print = pd.ShowDialog();
if (print == true)
{
XpsDocument xpsDocument = new XpsDocument("C:\\YourDocumentFullPath\\DocumentName.xps", FileAccess.ReadWrite);
FixedDocumentSequence fixedDocSeq = xpsDocument.GetFixedDocumentSequence();
pd.PrintDocument(fixedDocSeq.DocumentPaginator, "XPS Printing");
}