Sub Demo()
Application.ScreenUpdating = False
With ActiveDocument.Range
  With .Find
    .ClearFormatting
    .Replacement.ClearFormatting
    .Text = "[0-9]{1,4} [AB].[DC]."
    .Replacement.Text = ""
    .Forward = True
    .Format = False
    .Wrap = wdFindStop
    .MatchWildcards = True
    .Execute
  End With
  Do While .Find.Found
    If Split(.Text, " ")(1) = "B.C." Then
      .InsertAfter " (chinese year " & Split(.Text, " ")(0) + 2699 & ")"
    ElseIf Split(.Text, " ")(1) = "A.D." Then
      .InsertAfter " (chinese year " & Split(.Text, " ")(0) + 2698 & ")"
    End If
    .Collapse wdCollapseEnd
    .Find.Execute
  Loop
End With
Application.ScreenUpdating = True
End Sub