I'm currently working on a site that contains landing pages for articles with an abstract for each article and links to the full articles, which are PDFs which have been uploaded to the site. The abstracts are generally the first paragraphs of the full article. Since PDFs are indexed by Google, I assumed that dup content issues are as relevant for them as any other web page - is this incorrect? I'm thinking of implementing a canonical link element on the articles themselves. What are your thoughts on this?