This issue is caused by an error with Adobe Acrobat Reader's plugin, which will not allow documents to be printed within a browser.
To resolve this, you can do the following:
Open Adobe Acrobat Reader
Navigate to Edit, Preferences
In the new window, navigate to Security (Enhanced)
In the Sandbox Protections section, untick Enable Protected Mode at Startup
In the Enhanced Security section, untick Enable Enhanced Security
Press OK and restart Adobe Acrobat Reader