There is a special bookmark to work with a range (or select) for a full page
Code:
Sub GetLines()
Dim rng As Range
Set rng = ActiveDocument.GoTo(What:=wdGoToPage, Count:=3)
Set rng = rng.GoTo(What:=wdGoToBookmark, Name:="\page")
MsgBox rng.ComputeStatistics(wdStatisticLines)
End Sub