There are many methods and libraries that would help you in creating a PDF file using C# code in ASP.NET website. iTextSharp is one of them which is a usefull library for creating a PDF from HTML.
Have a look at the following CodeProject
article[
^], although it is in VB.NET, but it will give you an overview of using iTextSharp library. Get the iTextSharp library at
sourceforge[
^].
For a quick guide, read this
article[
^] and go to the Quick Example section of it. It has a really very quick example of converting the web page to a pdf.
Finally, read this previous
question[
^].