Not sure what you mean. What's "upub"? And I hope you are aware that even if it were possible technically, there would be certain imperatives going on regarding copyrights and other IP rights. So whatever you are looking to do is probably not a good idea in the first place...
I purchased a barnes and noble ebook but can't read it on my pc - its a
upub file. Thanks for your response but I will address my concern to those
who have an answer.
You can find the Nook Reading Apps at http://www.barnesandnoble.com/u/Getting-Started-NOOK-Reading-Apps/379003552. This will allow you to view your purchased content on your computer.
As for converting the content to a PDF that would require defeating the Digital Rights Management for your purchased content. You will want to go to a different source in order to determine the steps to do so.
Moving this topic to the Adobe Digital Editions forum.