I found it.
http://www.telerik.com/help/silverlight/radrichtextbox-features-import-export.html
together with
http://www.telerik.com/help/silverlight/radrichtextbox-features-document-elements-raddocument.html
showed me how to do it.
here is a code snippit:
private void PrintToPDF()
{
Section section = new Section();
Paragraph paragraph = new Paragraph();
InlineUIContainer container = new InlineUIContainer();
container.UiElement = new PrintLayout(this.map);
container.Height = 400;
container.Width = 400;
paragraph.Inlines.Add(container);
section.Blocks.Add(paragraph);
RadDocument document = new RadDocument();
document.DefaultPageLayoutSettings = new PageLayoutSettings(PaperTypes.Letter);
document.Children.Add(section);
PdfFormatProvider provider = new PdfFormatProvider();
string extension = "pdf";
SaveFileDialog dialog = new SaveFileDialog()
{
DefaultExt = extension,
Filter = String.Format("{1} file (*.{0})|*.{0}|All files (*.*)|*.*", extension, "PDF"),
FilterIndex = 1
};
bool? dialogResult = dialog.ShowDialog();
if (dialogResult == true)
{
using (Stream output = dialog.OpenFile())
{
provider.Export(document, output);
MessageBox.Show("Saved Successfuly!");
}
}
}