Convert Manual Numbering 1.0, 1.1, 1.1.1, 1.1.2 to automatic numbering - Word 2007 VBA Macro

You will need to have appropriately defined Heading styles in the template and then the following should work

Selection.HomeKey wdStory
 With Selection.Find
     Do While .Execute(FindText:="[0-9]{1,}.[0-9]{1,}.[0-9]{1,}.[1-9]{1,}^t[A-z]{1,}", Forward:=True, _
     MatchWildcards:=True, Wrap:=wdFindContinue) = True
         With Selection
             .Paragraphs(1).Style = wdStyleHeading4
             .text = Mid(.text, InStr(.text, vbTab) + 1)
         End With
     Loop
 End With
 With Selection.Find
     Do While .Execute(FindText:="[0-9]{1,}.[0-9]{1,}.[1-9]{1,}^t[A-z]{1,}", Forward:=True, _
     MatchWildcards:=True, Wrap:=wdFindContinue) = True
         With Selection
             .Paragraphs(1).Style = wdStyleHeading3
             .text = Mid(.text, InStr(.text, vbTab) + 1)
         End With
     Loop
 End With
 With Selection.Find
     Do While .Execute(FindText:="[0-9]{1,}.[1-9]{1,}^t[A-z]{1,}", Forward:=True, _
     MatchWildcards:=True, Wrap:=wdFindContinue) = True
         With Selection
             .Paragraphs(1).Style = wdStyleHeading2
             .text = Mid(.text, InStr(.text, vbTab) + 1)
         End With
     Loop
 End With
 With Selection.Find
     Do While .Execute(FindText:="[0-9]{1,}.0^t", Forward:=True, _
     MatchWildcards:=True, Wrap:=wdFindContinue) = True
         With Selection
             .Paragraphs(1).Style = wdStyleHeading1
             .text = Mid(.text, InStr(.text, vbTab) + 1)
         End With
     Loop
 End With

Try:

Sub ApplyHeadingStyles()
Dim Para As Paragraph, Rng As Range, iLvl As Long
With ActiveDocument.Range
  For Each Para In .Paragraphs
    Set Rng = Para.Range.Words.First
    With Rng
      If IsNumeric(.Text) Then
        While .Characters.Last.Next.Text Like "[0-9. " & vbTab & "]"
          .End = .End + 1
        Wend
        iLvl = UBound(Split(.Text, "."))
        If IsNumeric(Split(.Text, ".")(UBound(Split(.Text, ".")))) Then iLvl = iLvl + 1
        If iLvl < 10 Then
          .Text = vbNullString
          Para.Style = "Heading " & iLvl
        End If
      End If
    End With
  Next
End With
End Sub

Note: the above macro assumes the headings are linked to the numbering levels. If your heading Styles lack the auto multi-level list numbering, you can re-apply it via the following macro. As coded, the headings are also indented (in 0.5cm increments) according to their level.

Sub ApplyMultiLevelHeadingNumbers()
Dim LT As ListTemplate, i As Long
Set LT = ActiveDocument.ListTemplates.Add(OutlineNumbered:=True)
For i = 1 To 9
  With LT.ListLevels(i)
    .NumberFormat = Choose(i, "%1", "%1.%2", "%1.%2.%3", "%1.%2.%3.%4", "%1.%2.%3.%4.%5", "%1.%2.%3.%4.%5.%6", "%1.%2.%3.%4.%5.%6.%7", "%1.%2.%3.%4.%5.%6.%7.%8", "%1.%2.%3.%4.%5.%6.%7.%8.%9")
    .TrailingCharacter = wdTrailingTab
    .NumberStyle = wdListNumberStyleArabic
    .NumberPosition = CentimetersToPoints(0)
    .Alignment = wdListLevelAlignLeft
    .TextPosition = CentimetersToPoints(0.5 + i * 0.5)
    .ResetOnHigher = True
    .StartAt = 1
    .LinkedStyle = "Heading " & i
  End With
Next
End Sub