If you see a black screen when trying to view a PDF, like the image below, you likely have a Google Chrome browser extension that is blocking it from opening.
Step 1: Try without any extensions
You can easily confirm that the extensions are the cause of the problem by loading the PDF from the Incognito window. If the PDF loads correctly, one of your extensions is at fault.
To open an Incognito window:
On Windows, press "Ctrl" + "Shift" + "N".
On MAC, press "CMD" + "Shift" + "N".
After opening an incognito window, log in and try to load a PDF. If it works, you now know one of your extensions is the problem.
Process of elimination
You can toggle your extensions on and off by heading to chrome://extensions/.
Switch these off one at a time to see which one is stopping the PDF from loading.
Some reported extensions that are linked to this problem are:
McAfee Websafe
McAfee WebAdvisor
Grammarly
Keeping the troublesome extension
If it isn't feasible to turn off or change the extension, right-click the grey/black area where the PDF should be and click "Save as".
This will make the PDF become visible, rather than offer a means to save the file (another quirk of the extension). From here, you can then save the PDF in the normal way.