To disable the Chrome pdf viewer and allow the OP Form to download and be opened by pdf view please follow the directions below.

1. Click on Chrome menu, select Settings2. Scroll down and click on Advanced3. Under Privacy & Security, click on Content Settings,4. Scroll down and click on PDF Documents or visit chrome://settings/content/pdfDocuments
  • To disable Chrome PDF Viewer, turn on ‘Download PDF files instead of automatically opening them in Chrome’ Setting,
  • To enable PDF Viewer, you need to turn off the above mentioned setting. 
disable Chrome PDF Viewer Done! Chrome Internal PDF Viewer will be enabled/disabled as per the setting chosen by you.