how to provide SAVE(ctrl +S) fuction to rich text editor

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VS2008

C#

Visual-Studio

WPF

I am developing a rich text editor in wpf.its save as function work perfectly but i also want to provide save option which save the already open document with same name at same location like a notepad or word save option...
i am posting my source code here plz help me..

.Xaml file

<RichTextBox Height="420.724" Margin="6,66,6,5.999" Name="txtcreatelssn" Width="642" VerticalScrollBarVisibility="Visible" HorizontalScrollBarVisibility="Auto" SpellCheck.IsEnabled="True"/>
                            <ToolBar Height="34" Margin="6,34,6,0" Name="toolBarMenu" VerticalAlignment="Top" >
                                <Button Click="CmdNew" >
                                    <Image Source="/MTDLL_TEACHER;component/Images/filenew.png" >
                                    </Image>
                                </Button>
                                <Button x:Name="Open" Click="Open1"  >
                                    <Image Source="/MTDLL_TEACHER;component/Images/fileopen.png" ></Image>
                                </Button>
                                <Button  x:Name="Save_As" Click="save_as">
                                    <Image Source="/MTDLL_TEACHER;component/Images/filesave.png"></Image>
                                </Button>
                                <Button  x:Name="Save" Click="save">
                                    <Image Source="/MTDLL_TEACHER;component/Images/filesaveas.png"></Image>
                                </Button>
                                <Button  Command="Cut" ToolTip="Cut">
                                    <Image Source="/MTDLL_TEACHER;component/Images/editcut.png"></Image>
                                </Button>
                                <Button  Command="Copy" ToolTip="Copy">
                                    <Image Source="/MTDLL_TEACHER;component/Images/editcopy.png"></Image>
                                </Button>
                                <Button  Command="Paste" ToolTip="Paste">
                                    <Image Source="/MTDLL_TEACHER;component/Images/editpaste.png"></Image>
                                </Button>
                                <Button  Command="Undo" ToolTip="Undo">
                                    <Image Source="/MTDLL_TEACHER;component/Images/editundo.png"></Image>
                                </Button>
                                <Button  Command="Redo" ToolTip="Redo">
                                    <Image Source="/MTDLL_TEACHER;component/Images/editredo.png"></Image>
                                </Button>
                                <Button  Command="EditingCommands.ToggleBold" ToolTip="Bold">
                                    <TextBlock FontWeight="Bold" FontSize="15" Foreground="Black">B</TextBlock>
                                </Button>
                                <Button  Command="EditingCommands.ToggleItalic" ToolTip="Italic">
                                    <TextBlock FontStyle="Italic" FontWeight="Bold" FontSize="15" Foreground="Black">I</TextBlock>
                                </Button>
                                <Button  Command="EditingCommands.ToggleUnderline" ToolTip="Underline">
                                    <TextBlock TextDecorations="Underline" FontWeight="Bold" FontSize="15" Foreground="Black">U</TextBlock>
                                </Button>
                                <Button  Command="EditingCommands.AlignLeft" ToolTip="Align Left">
                                    <Image Source="/MTDLL_TEACHER;component/Images/paragraphleftjustify.png"/>
                                </Button>
                                <Button  Command="EditingCommands.AlignCenter" ToolTip="Align Center">
                                    <Image Source="/MTDLL_TEACHER;component/Images/paragraphcenterjustify.png"/>
                                </Button>
                                <Button  Command="EditingCommands.AlignRight" ToolTip="Align Right">
                                    <Image Source="/MTDLL_TEACHER;component/Images/paragraphrightjustify.png"/>
                                </Button>
                            </ToolBar>

.Xaml.cs file

#region wordfunctionality

       void CmdNew(object sender, RoutedEventArgs e)
       {
           txtcreatelssn.Document = new FlowDocument();
       }
       void Open1(object sender, RoutedEventArgs e)
       {
           System.Windows.Forms.OpenFileDialog openFile = new System.Windows.Forms.OpenFileDialog();
           openFile.Filter = "RichText Files (*.rtf)|*.rtf|All Files (*.*)|*.*";

           if (openFile.ShowDialog() == System.Windows.Forms.DialogResult.OK)
           {
               // Create a TextRange around the entire document.
               TextRange documentTextRange = new TextRange(txtcreatelssn.Document.ContentStart, txtcreatelssn.Document.ContentEnd);

               using (FileStream fs = File.Open(openFile.FileName, FileMode.Open))
               {
                   if (System.IO.Path.GetExtension(openFile.FileName).ToLower() == ".rtf")
                   {
                       documentTextRange.Load(fs, System.Windows.DataFormats.Rtf);
                   }
                   else
                   {
                       documentTextRange.Load(fs, System.Windows.DataFormats.Xaml);
                   }
               }

           }
       }

       void save_as(object sender, RoutedEventArgs e)
       {
           System.Windows.Forms.SaveFileDialog savefile = new System.Windows.Forms.SaveFileDialog();
           //System.Windows.Forms.OpenFileDialog openFile = new System.Windows.Forms.OpenFileDialog();
           savefile.Filter = "RichText Files (*.rtf)|*.rtf|All Files (*.*)|*.*";

           if (savefile.ShowDialog() == System.Windows.Forms.DialogResult.OK)
           {
               // Create a TextRange around the entire document.
               TextRange documentTextRange = new TextRange(
                   txtcreatelssn.Document.ContentStart, txtcreatelssn.Document.ContentEnd);
               MemoryStream ms = new MemoryStream();
               // If this file exists, it's overwritten.
               using (FileStream fs = File.Create(savefile.FileName))
               {
                   if (System.IO.Path.GetExtension(savefile.FileName).ToLower() == ".rtf")
                   {
                       documentTextRange.Save(fs,System.Windows.DataFormats.Rtf);
                   }
                   else
                   {
                       documentTextRange.Save(fs, System.Windows.DataFormats.Xaml);


                   }
               }

           }

       }//save_as

       #endregion wordfunctionality