I have solved it. Thanks for your time anyway.
Protected Sub PrintBtn_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles PrintBtn.Click
Dim psiPrint As New System.Diagnostics.ProcessStartInfo()
psiPrint.Verb = "print"
psiPrint.WindowStyle = ProcessWindowStyle.Hidden
psiPrint.FileName = Server.MapPath("~\Form\Form.pdf")
psiPrint.UseShellExecute = True
System.Diagnostics.Process.Start(psiPrint)
End Sub