You could omit the count of spaces, line breaks and paragraph returns
with something like:
Sub CountCharacters()
Dim oChr As Range
Dim i As Long
For Each oChr In
ActiveDocument.Sections(1).Headers(wdHeaderFooterPrimary).Range.Characters
Select Case Asc(oChr)
Case Is = 11, 13, 32 'The Asc Code for a paragraph, line break, and
space
i = i
Case Else
i = i + 1
End Select
Next
MsgBox "The header contains " & i & " characters."
End Sub