Add the following lines in your code.
Dim rpt As New rptReportFileName
rpt.PrintOptions.PaperSize = CrystalDecisions.Shared.PaperSize.PaperA4
rpt.PrintOptions.PaperOrientation = CrystalDecisions.Shared.PaperOrientation.Portrait
You may need to add the following reference to your project.
CrystalDecisions.Shared
It works for me.