Suggest correction in code to render report

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VB

SSRS

PDF

Hi,
I was suggested the following code to programmatically render SSRS report in PDF format.
I tried it but it is not working.

Can any body suggest what might be required?
Thanks

Dim format As String = "PDF"
        Dim fileName As String = "C:\Output.pdf"
         Dim reportPath As String = "/[Report Folder]/Invoice"

        ' Prepare Render arguments
        Dim historyID As String = Nothing
        Dim deviceInfo As String = Nothing
        Dim extension As String = Nothing
        Dim encoding As String
        Dim mimeType As String = "application/pdf"
        Dim warnings() As Microsoft.Reporting.WinForms.Warning = Nothing
        Dim streamIDs() As String = Nothing
        Dim results() As Byte

        ReportViewer1.LocalReport.Render(format, deviceInfo, mimeType, encoding, fileName, streamIDs, warnings)

      
        ' Open a file stream and write out the report
        Dim stream As FileStream = File.OpenWrite(fileName)
        stream.Write(results, 0, results.Length)
        stream.Close()