The only consideration I see is that the words download, PDF, and article will become likely the top three or at least within the top ten keywords your site is known for therefore the site topic as seen by Google and/or Bing maybe that of article download. There may be two problems with that:
Your site is not about article downloading. It can dilute the SEO effect of the other keywords your site is known for and the performance of any page on a page by page basis depending and performance overall.
Article sharing sites have been hit hard lately and algorithms exist to identify these sites. There may be a chance that your site will fall into this category. It may be a small chance, but in is in.
Pay attention to the Content Keywords in Google Webmaster Tools. It is critically important that these keywords reflect your site topic before SEO begins. It is the foundation upon which the rest of your work will rest upon.
If you find this is the case, perhaps you can have your cake and eat it too. Only in web design does this work. You can change your links to the PDFs from a text link to an image link and if you repeat the article title in the alt text, then you should be more than okay. In this case, it may be okay to use the terms download, PDF, and article too. Just make sure you are mixing up the alt text with the article title.