Do you want to generate an html file with a snapshot of the PDF inside it? Or do you want to convert the PDF contents to HTML contents (for example, if the PDF had a table, you want to generate an HTML file that has <table> tag)?
If you want the first, a while back I used an sdk called lead tools that enables you to convert the PDF to an image then embed it inside an HTML page. But if you want the second, I think you will have to parse the PDF element by element and write the code that converts each element to an HTML tag.