Some people don't like their browsers opening PDF document inside of it's window but want the PDF file saved to the hard drive instead.
This is also useful for Comodo Dragon which is based on Google Chrome.
Here's how do disable opening PDF files in Google Chrome:
- In Google Chrome copy & paste the following URL into the address bar: chrome://plugins/
- Under Plug-ins look for 'Chrome PDF Viewer'
- Click 'Disable'
- Close Settings and you're done