Using the Metro Reader app that comes with Win 8, you can right-click while viewing something like a PDF file and it will bring up a menu at the bottom of the page. There are various selections on that menu, one of which is a button to Print the file. Click on More to find the Close File option. If using a touch screen instead of a mouse, long press on the screen to bring up the menu.
You can close any of the Metro apps by moving the mouse pointer to the top of the screen and it will turn from an arrowhead to a hand. When it turns to a hand, click and hold, then drag the hand all the way to the bottom of the screen which will close the app. If using a touch screen, touch the top of the screen and drag your finger all the way down...