Pass Authenticated Session In Another Request in ASP.NET

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I am using ABCPDF.net to render my HTML to PDF pages, but I want to protect these using the current authenticated session. However, the request to get the HTML to render the PDF doesnt carry over the session, but creates a new one. I am using ASP.NET Membership, and passwigin the session ID and creating a cookie on the ASP.NET request.\[code\] var sessionId = HttpUtility.ParseQueryString(Url)["sid"]; if(sessionId != null) { doc.HtmlOptions.HttpAdditionalHeaders = string.Format("Cookie: ASP.NET_SessionId={0}", sessionId); }\[/code\]I read this in ABCPDF.net documentation and am doing just that, but the request always uses a different session.httpadditionalheadersDo I need to pass something else, or can I do something else?