The link Garth offered led to the solution. c# - Display ASP.NET generated pdf byte to web page without saving the file - Stack Overflow
There were a few others offered for how to do it with an MVC web site but only that page led me to how to do it with a normal ASP.Net Razor page. Essentially the solution, for anyone that might find this, worked both as an object and as an embed. My C# code was something like:
byte bPDF = File.ReadAllBytes("filename.pdf");
string base64PDF = System.Convert.ToBase64String(bPDF, 0, bPDF.Length);
wrapped in string str = "<embed src="data:application/pdf;base64, " + ...getPDFAsBase64() + "" type="application/pdf" width="100%" height="800px" />";
My Razor code was [html][body] @Html.Raw(PDFModel.strReturnPDF()) [/body][/html].
It displayed the full height PDF, 51 pages.
Now I just need to read it from an S3 bucket and serve it from a Lambda encased "web site".