C# - Request Is Not Available For PDF Request?

We're trying to create a .NET aspx page that will have a PDF within it. Doing this by hardcoding it is easy.

<object height="1250px" width="100%" type="application/pdf" data="our.pdf">
<param value="our.pdf" name="src" />
<param value="transparent" name="wmode" />
</object>

(don't worry too much about the transparent thing...we're doing that for other reasons...but I include it here "just in case".)The problem is when we want to generate the PDF dynamically. Our code to populate the literal on the front end looks like this:

ltrPDF.Text = String.Format("<object height="1250px" width="100%" type="application/pdf" data="ourPdfGenerator.aspx?var0={0}&var1={1}&var2={2}">", var0, var1, var2);
ltrPDF.Text += String.Format("<param value="ourPdfGenerator.aspx?var0={0}&var1={1}&var2={2}">", var0, var1, var2);
ltrPDF.Text += "<param value="transparent" name="wmode"/>";
ltrPDF.Text += "</object>";

Kind of ugly, but it seems like it should work. But it doesn't.When I debug, and put a breakpoint on the first line of ourPdfGenerator.aspx.cs Page_Load method, I reach the breakpoint without any difficulty. However, the first thing we do is try to use Request.QueryString:

string var0 = Request.QueryString["var0"];

which immediately throws an HttpException: "Request is not available in this context." I'm not clear on:

Why isn't it available? What can I do about it?

EDIT: (as an aside, I know it seems a bit weird to ask for a mime-type of pdf from a aspx page...but we've used an aspx page to generate cs pages before...we do something like this:

Response.Clear();
Response.ContentType = "application/pdf";
Response.AddHeader("Content-Disposition", "attachment;filename="our.pdf"");[code].....

And this has been working fine in other contexts for a while...but always as its own page. What we're doing differently now is instead of having this page called directly, we're trying to embed it, so it's being called from the <object> tag, which is apparently causing problems...