Sub Demo()
Application.ScreenUpdating = False
Dim StrFnd As String
Options.DefaultHighlightColorIndex = wdYellow
StrFnd = InputBox("What is the text to highlight?")
If Trim(StrFnd) = "" Then Exit Sub
With ActiveDocument.Range.Find
  .ClearFormatting
  .Replacement.ClearFormatting
  .Replacement.Highlight = True
  .Text = StrFnd
  .Replacement.Text = "^&"
  .Format = True
  .Forward = True
  .MatchCase = True
  .MatchWildcards = False
  .Wrap = wdFindContinue
  .Execute Replace:=wdReplaceAll
End With
Application.ScreenUpdating = True
End Sub