There are no 'lines' in a Word document. Lines are created by formatting text to the margins and if you select such a line and reformat it, the chances are that it will occupy a different space to that it previously occupied. In the context of this I would hope by 'line' that you mean paragraph, in which case it is relatively straightforward

Sub aFindPriSub()Dim Rng As Range
    Set Rng = ActiveDocument.Range
    With Rng.Find
        .ClearFormatting
        Do While .Execute(findText:="Sub", Forward:=True, _
                          Format:=False, Wrap:=wdFindStop)
            With Rng
                .Start = Rng.Paragraphs(1).Range.Start
                .End = Rng.Paragraphs(1).Range.End - 1
                With .Font
                    .Italic = False
                    .Bold = True
                    .TextColor = RGB(0, 176, 240)
                End With
                .Collapse 0
            End With
        Loop
    End With
    Set Rng = Nothing
End Sub