Is this duplicate content?

Your website has 100 articles. You put each of those 100 articles in PDF files and put those PDF files into your website. Would Google consider this as duplicate content?

Google can read PDF's, so I imagine there may be some issues although I have several sites where readers prefer to download material for reading or printing out so provide PDF links at the bottom of the articles and have never had any problems although I do prevent them from indexing via the robots.txt.

Sorry can't provide a definitive answer on this but I would say better to be safe than sorry.