Thanks for your inquiry. Perhaps, you’re using an older version of Aspose.Words. I would suggest you please upgrade to the latest version of Aspose.Words i.e. 11.2.0 from the following link:
Your example, isn’t quite what we need here. We take the doc and save the output as a .pdf, not a .doc file. When we use your example and have the outputfilename = Document.doc it pops up a window asking to OPEN or SAVE and it is named ok. However, if our output id DocumentName.pdf, it loaded the PDF in the browser window, and the SAVE still picked up the aspx name instead of DocumentName.pdf
Please make sure you are referencing the Aspose.Words DLLs under the .net2.0 folder. Using this DLL you should see the method overload Awais is talking about.