Private Sub FixStyles()
    Dim stlStyle As Style
    Dim arrTemplateStyles() As Style ' This array would contain all the styles saved in the template
    ' Maybe there's a built-in collection that has these values and makes this variable unnecessary
    
    ' Iterate through all the styles in the current document
    For Each stlStyle In ActiveDocument.Styles
        ' If the style is not in the list of styles saved in the attached template
        If Not SearchInArray(stlStyle.NameLocal, arrTemplateStyles) Then
            ' Delete said style and go on with the next one
            Delete stlStyle
        End If
    Next stlTemplateStyle
End Sub

Private Function SearchInArray(strName As String, varArray As Variant) As Boolean
    ' Function used to look for a specific item in an array
    Dim blnFound As Boolean
    Dim varItem As Variant
    blnFound = False
    
    For Each varItem In varArray
        If varItem.NameLocal = strName Then
            blnFound = True
            Exit For
        End If
    Next varItem
    SearchInArray = blnEncontrado
End Function

Sub ScratchMacro()
'A basic Word Macro coded by Gregory K. Maxey
Dim oStyle As Style, oStyleValidate As Style
Dim oDocValidate As Document
Dim oTmp As Template
  Set oTmp = ActiveDocument.AttachedTemplate
  Set oDocValidate = oTmp.OpenAsDocument
  Set oStyle = ActiveDocument.Styles("Style1")
  For Each oStyle In ActiveDocument.Styles
    On Error Resume Next
    Set oStyleValidate = oDocValidate.Styles(oStyle.NameLocal)
    If Err.Number <> 0 Then
      oStyle.Delete
      Err.Clear
    End If
  Next oStyle
  oDocValidate.Close wdDoNotSaveChanges
lbl_Exit:
  Exit Sub
End Sub