Any document creation software that can save documents as PDF can save them as HTML. I'm assuming the issue is that your users will be creating rich documents (lots of embedded images), which results in multiple files, and your requirements stem from a desire to make uploading these documents as simple as possible to the user.

There are numerous conversion packages that can probably do this for you, however when you're talking about rich content, you are talking about text plus images. Those images have to be stored somewhere and served somehow, and whatever conversion method you use will require you to examine all image sources to make sure they point to valid locations on your server.

I would like to suggest an alternate way of doing this that you can take to your team: Implement one of the many blog APIs for publishing content. There are free and commercial software packages that use these APIs to publish content directly to a website, such as Windows Live Writer and Microsoft Word. Your users can simply create their content and upload it directly to your website without having to publish it as PDF first then upload it. So the process becomes much smoother for your users, and you get the posts in a form that doesn't require you spend thousands of dollars on developing or buying conversion code.

The two most common APIs are the MetaWeblog API and the Movable Type API. Both are very simple and easy to implement. I think this way would be a MUCH better alternative than what you're thinking about doing.