I have a Dell Inspiron 15 5000 Series that I bought November 2016. I have an article sent to me as a PDF sideways, so I pressed Ctrl + Alt + left arrow and nothing happened. My laptop has Windows 10 Version 1703.

This hot key is a feature of your graphics driver. Newer versions of it discontinued use of these hot keys. You may check this option if it is still available by pressing Ctrl + Alt + F12 > Options and Support > Hot Key