Assuming you have already defined the original document and newDoc then you could try this
Code:
Sub aTest()
Dim aRng As Range, aDoc As Document, newDoc As Document
'I'll assume you have already set aDoc and newDoc to specific documents
With newDoc.Range.Find
.Text = "^t"
.Replacement.Text = " "
.Forward = True
.Wrap = wdFindStop
.Format = False
.MatchCase = False
.MatchWholeWord = False
.MatchWildcards = False
.MatchSoundsLike = False
.MatchAllWordForms = False
.Execute Replace:=wdReplaceAll
End With
Set aRng = aDoc.Range
aRng.Collapse Direction:=wdCollapseEnd
aRng.FormattedText = newDoc.Range.FormattedText
End Sub