We using this type of format for PDF 2008.
Imports SQL2008
Protected Sub btnGuardar_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnGuardar.Click
Dim rs As New ReportExecutionService()
rs.Credentials = System.Net.CredentialCache.DefaultCredentials
rs.Url = System.Configuration.ConfigurationManager.AppSettings("sql2008.ReportExecution2005")
Dim archivo As String = "C:\Users\elopez\Documents\AMAG\_SGC\pdfGenerado\certificado.pdf"
Dim formato As String = "PDF"
Dim history As String = Nothing
' Render arguments
Dim resultado As Byte() = Nothing
Dim reportPath As String = "/ServerReports/" & ReportName
Dim format As String = "PDF"
Dim historyID As String = Nothing
Dim devInfo As String = "<DeviceInfo><StreamRoot>/RSWebServiceXS/</StreamRoot></DeviceInfo>"
Dim encoding As String = Nothing
Dim mimeType As String = Nothing
Dim warnings As SQL2008.Warning() = Nothing
Dim streamIDs As String() = Nothing
Dim execInfo As New ExecutionInfo
Dim execHeader As New ExecutionHeader
Dim extension As String = ""
resultado = rs.Render(formato, devInfo, extension, mimeType, encoding, warnings, streamIDs)
Response.ClearContent()
Response.ContentType = "application/pdf"
Response.BinaryWrite(resultado)
Response.Flush()
End Sub