How to correct the error" Name 'ActiveDocument' is not declared."

 
 Public Class Form1
 
     ' Three simple macros to implement a secondary clipboard
 
     ' Global to act as clipboard
     Dim g_lpszSecondClipBoard = ""
 
 
     Sub SecondaryClipBoardCut()
         'DESCRIPTION: Performs a cut of current selection to a secondary clipboard.
         g_lpszSecondClipBoard = ActiveDocument.Selection.Text
         ActiveDocument.Selection.Text = ""
     End Sub
 
     Sub SecondaryClipBoardCopy()
         'DESCRIPTION: Performs a copy of current selection to a secondary clipboard.
         g_lpszSecondClipBoard = ActiveDocument.Selection
     End Sub
 
     Sub SecondaryClipBoardPaste()
         'DESCRIPTION: Performs a paste of secondary clipboard to the current selection.
         ActiveDocument.Selection = g_lpszSecondClipBoard
     End Sub
 
 
     Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
         SecondaryClipBoardCut()
     End Sub
 
     Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
         SecondaryClipBoardCopy()
     End Sub
 
     Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
         SecondaryClipBoardPaste()
     End Sub
 End Class