Subscript numbers in chemical formulae from selection

I often find chemical formulae in my documents that require the numbers to be made subscript. e.g. H2O should be H₂O and H2SO4 should be H₂SO₄. I am trying to write a macro that will take numbers from a highlighted selection and subscript numerical values. I am not very good at programming. I have tried variations on the following:

Sub SubscriptNumbers()
    
    Dim Char As String
  
    For Each Char In Selection.Characters
             
            If Char >= "0" And Char <= "9" Then
                Char = Char.Font.Subscript
            End If
        
    Next Char
    
End Sub

But I get confusing errors (Compile Error: For Each control variable must be Variant or Object; but if I change Char to variant, it runs without error but doesn't appear to do anything). I know that there is an aversion from people in the know about using 'Select' but my doc will likely contain lots of other numbers that should not be made subscript.

Although not stated in the documentation to loop through Characters you need to declare Char As Range. You then need to check if Char.Text is a number. There is a built-in function for doing this - IsNumeric. Finally you need to set .Font.Subscript to either true or false.

Sub SubscriptNumbers()
   Dim Char As Range
  
   For Each Char In Selection.Characters
      If IsNumeric(Char.Text) Then
         Char.Font.Subscript = True
      End If
   Next Char
    
End Sub