Question

How to get message onto a html page after processing from ashx page?

Answer 1

Normally, when you link a file that file will always display inside of the browser because the browser loads it and automatically determines the content type based on the file extension. The Web Server provides a content type based on mime-type mappings, and based on that content type the browser serves the page and displays it.

So when you click on a link like a jpg image the browser knows it's an image and will display that image. You can of course always use the browser short cut menu and use the Save Target As option to save the file to disk.
I hope this will help you