private void Form1_Load(object sender, System.EventArgs e)
{
    rptOne rpt1 = new rptOne();
    rpt1.Run();
    rptTwo rpt2 = new rptTwo();
    rpt2.Run();
    rpt1.Document.Pages.AddRange(rpt2.Document.Pages);
    viewer1.Document = rpt1.Document;
}

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Dim rpt As New rptOne()
        rpt.Run()
        Dim rpt2 As New rptTwo()
        rpt2.Run()
        rpt.Document.Pages.AddRange(rpt2.Document.Pages)
        Viewer1.Document = rpt.Document
End Sub