how to speed up word 2007 automation

Imports Word = Microsoft.Office.Interop.Word
Imports System.Runtime.InteropServices
   Dim oWord As Word.Application
     Dim oDoc As Word.Document
     oWord = CreateObject("Word.Application")
         oDoc = oWord.Documents.Open("Test.doc")
          oWord.Visible = False
         oDoc.SpellingChecked = False
         oWord.ScreenUpdating = False
         oWord.CheckLanguage = False
         oDoc.GrammarChecked = False
         oWord.AutoCorrect.CorrectCapsLock = False
         oWord.AutoCorrect.CorrectDays = False
         oWord.AutoCorrect.CorrectHangulAndAlphabet = False
         oWord.AutoCorrect.CorrectInitialCaps = False
         oWord.AutoCorrect.CorrectKeyboardSetting = False
         oWord.AutoCorrect.CorrectSentenceCaps = False

  sReplace = "AbCD"
ofind = oWord.Selection.Find
  For Each oPara1 In oWord.ActiveDocument.Paragraphs
               myRange = oPara1.Range
               Dim str1 As String = oPara1.Range.Text
               Dim str2 As String = Midstr(str1)'remove space form string
               If str2 <> Nothing Then
                   bResult = IsUnicode(str2)
                   If bResult = True Then
                   Else
                       With ofind
                           .ClearFormatting()
                           .Text = str2
                           .Replacement.ClearFormatting()
                           .Replacement.Text = sReplace
                           .MatchCase = True
                           .MatchWholeWord = True
                           .Wrap = Word.WdFindWrap.wdFindContinue
                           .Execute(Replace:=Word.WdReplace.wdReplaceAll)
                       End With
                   End If

               End If
               oWord.Selection.MoveDown(Unit:=Word.WdUnits.wdParagraph, Count:=1)
           Next