Workaround: until the feature be implemented one can print each page individually respecting its orientation whether it is portrait or landscape
public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
 
        this.radPdfViewer1.LoadDocument(@"..\..\sample.pdf");
    }
 
    private void radButton1_Click(object sender, EventArgs e)
    {
        RadPrintDocument doc = new RadPrintDocument();
        doc.AssociatedObject = this.radPdfViewer1;
 
        for (int i = 0; i < this.radPdfViewer1.Document.Pages.Count; i++)
        {
            RadFixedPage page = this.radPdfViewer1.Document.Pages[i];
 
            doc.CurrentPage = i;
            doc.PrinterSettings.PrintRange = PrintRange.CurrentPage;
            doc.Landscape = page.ActualWidth > page.ActualHeight;
 
            doc.Print();
        }
    }
}

RadPdfViewer can not display annotated PDF file
 Kindly,i used VintaSoft SDk to Annotate PDF File, File is annotated successfully and i can open it with Adobe Reader and see annotations is added to it
 but while i try to view annotated PDF file using RadPDFViewer File will displayed without annotations ,only original content displayed.
Kindly find my attached AnnotatedPDFfile To be loaded in RadPDfViewer

RadPdfViewer can not display annotated PDF file
 Kindly,i used VintaSoft SDk to Annotate PDF File, File is annotated successfully and i can open it with Adobe Reader and see annotations is added to it
 but while i try to view annotated PDF file using RadPDFViewer File will displayed without annotations ,only original content displayed.
Kindly find my attached AnnotatedPDFfile To be loaded in RadPDfViewer

Add two additional buttons in the RadPdfViewerNavigator like in Adobe Reader:
- The first one must fill the window with each page and scroll through pages continuously. 
- The second one must show one page at a time.

http://docs.telerik.com/devtools/wpf/controls/radpdfviewer/document-model/exceptionhandling

ADD. RadPdfViewer - add ability to show the document pages as thumbnails

Add rotate view button.

radPdfViewer1.PdfViewerElement.Find("keyword", PageNumber);

Resolution: 
You can use the following code snippet: 
radPdfViewer1.PdfViewerElement.Find(string text, int pageNumber)

Description: Single Page View Displays one page at a time, with no portion on other pages visible.

ADD. RadPdfViewer - add support for data fields

This issue can be observed when the text is too big to fit in cell.

FIX. RadPdfViewer - add option for unloading documents. Make sure that manipulating with the file is possible after being unloaded.