Sorry but that is not something I would ever include in mojoPortal. Even the author of the C# wrapper explains that it is not safe for a multi threaded environment like a web application, he processes the files by a windows service.
Also P/Invoking against a native dll will not work in medium trust hosting.
So it is the kind of thing where you would only use the web to manage a queue of urls to be processed into pdf and then the windows service could generate the pdf and put it somewhere so it was available for download in the web app. One could do that kind of thing as a custom feature and a custom windows service if you had full control of the server, but its not a candidate for inclusion in mojoPortal.
Best,
Joe