This can be done without Macros by converting *through* bullet lists.
1) type or paste your tabbed text outline in word:

2) convert tabs to bullets lists:

3) remove (set to "none") bullets:

4) convert of tabs to indents completed:

Create new vbs macro and run to convert from indents to tabs.
Sub indents2tabs()
Dim p As Paragraph
Set hash = CreateObject("Scripting.Dictionary")
tabcount = 0
lineindent = 0
Application.ScreenUpdating = False 'close screen and refresh
'cycling in the pragraphs of the active document
For Each p In ActiveDocument.Paragraphs
linetext = p.Range.Text
previouslineindent = lineindent
lineindent = p.LeftIndent
'MsgBox (lineindent & " = " & linetext)
If lineindent > 0 Then
'MsgBox ("do something")
p.LeftIndent = 0
If lineindent > previouslineindent Then
If hash.Item(lineindent) Then
tabcount = hash.Item(lineindent)
'MsgBox ("already got it:" & lineindent & "=" & hash.Item(lineindent))
Else
tabcount = tabcount + 1
hash.Item(lineindent) = tabcount
End If
End If
If lineindent < previouslineindent Then
If hash.Item(lineindent) Then
tabcount = hash.Item(lineindent)
'MsgBox ("already got it:" & lineindent & "=" & hash.Item(lineindent))
Else
tabcount = tabcount - 1
hash.Item(lineindent) = tabcount
End If
End If
If lineindent = previouslineindent Then
If hash.Item(lineindent) Then
tabcount = hash.Item(lineindent)
'MsgBox ("already got it:" & lineindent & "=" & hash.Item(lineindent))
Else
'tabcount = tabcount
hash.Item(lineindent) = tabcount
End If
End If
p.Range.InsertBefore (String(tabcount, Chr(9)))
'p.Range.InsertBefore (String(tabcount, Chr(9)) & lineindent & "/" & tabcount)
End If
Next p
Application.ScreenUpdating = True 'restore screen and refresh
End Sub