http://www.techradar.com/news/the-best-free-pdf-reader

A dedicated free PDF reader will let you do so much more than just open documents. If you want to merge several PDFs, convert them to a different format, extract images, tweak text or split them into individual pages, there's a free PDF reader that will make it straightforward.

Once you've installed a new PDF reader, it will display a prompt asking if you'd like to make it your default PDF reader. We recommend leaving your settings as they are until you've had a chance to try the new reader and see if it's right for you.