I assume that this code is run from Excel and that the userform name is TESTMASTER and the code is the code associated with the command button? In which case the following does work. (You will need to change the command button name).
Note that it works much faster if it doesn't have to open Word, so I have added code to use the open version if available. The code uses late binding to Word so it doesn't require a reference to the Word object library. I don't think that personally I would use DOC format or an Active X text box, but you may not have the option to change.
Private Sub CommandButton1_Click()
Dim wrdApp As Object
Dim wrdNNDF As Object
Dim FindWhat As Variant
Dim ReplaceWith As Variant
Dim i As Long
Dim bStarted As Boolean
Me.Hide
On Error Resume Next
Set wrdApp = GetObject(, "Word.Application")
If Err Then
Set wrdApp = CreateObject("Word.Application")
bStarted = True
End If
On Error GoTo 0
wrdApp.Visible = True
Set wrdNNDF = wrdApp.Documents.Open("C:\Review.doc")
wrdNNDF.Activate
'wrdApp.Visible = True
wrdApp.Selection.Find.ClearFormatting
wrdApp.Selection.Find.Replacement.ClearFormatting
FindWhat = Array("AAA", "CCC", "DDD")
ReplaceWith = Array(Me.tbox_Location.Text, Me.tbox_Comment.Text, Me.tbox_Comment.Text)
For i = 0 To 2
With wrdNNDF.Range.Find
.Text = FindWhat(i)
.Replacement.Text = ReplaceWith(i)
.Forward = True
.Wrap = 1
.Format = False
.MatchCase = False
.MatchWholeWord = False
.MatchWildcards = False
.MatchSoundsLike = False
.MatchAllWordForms = False
.Execute Replace:=2
End With
Next i
wrdNNDF.doc_RR_tbox_TGI.Text = TESTMASTER.tbox_Title.Text
wrdNNDF.PrintOut
wrdNNDF.Close SaveChanges:=0
If bStarted Then wrdApp.Quit
Unload Me
End Sub