The following replaces curly quotes with straight quotes.  It changes the
autocorrect option for "smart" quotes to straight quotes, goes through each
storyrange, replaces doulbe and single quotes with themselves, thus setting
them all straight.

Sub StraightenQuotes()

Dim rngStory As Range
Dim strString As String

'Set curly quotes to straight quotes
Options.AutoFormatAsYouTypeReplaceQuotes = False

For Each rngStory In ActiveDocument.StoryRanges
    Do Until (rngStory Is Nothing)
       If Len(rngStory) > 2 Then
           strString = Chr(34) 'double quotes
           GoSub FindReplace
           strString = Chr(39) 'single quotes
           GoSub FindReplace
       End If
      Set rngStory = rngStory.NextStoryRange
   Loop
Next rngStory

Exit Sub

FindReplace:

   With rngStory.Find
       .Text = strString
       .Replacement.Text = strString
       .Forward = True
       .Wrap = wdFindContinue
       .Format = False
       .MatchCase = False
       .MatchWholeWord = False
       .MatchAllWordForms = False
       .MatchSoundsLike = False
       .MatchWildcards = False
       .Execute Replace:=wdReplaceAll
   End With
   
   Return
   
End Sub