Open a music file and it'll open in Metro, a video it'll open in Metro and a picture file it'll open in Metro and this usually leads to user frustration…
Open a pdf and it'll open in Reader, open a second pdf and the first one will close down, goodbye multitasking. Unfortunately Microsoft have setup the defaults of Windows 8.1 to take you to the terrible Metro interface. You can 'Check display the All Apps view when I go to Start to bypass the user customisable Start Screen' if you prefer this screen however I won't do this as I will customise the Start Screen later on. It by default lists the annoying Metro Apps first so you need to scroll past them all the time when you want to open up something proper on your computer. To get to All Programs renamed 'App View' press the down arrow. The default user customisable screen is as shown below: I also prefer logging into the Desktop instead of Start and listing the Desktop Applications when the Apps view is listed. I prefer to disable the Metro interface when the mouse is moved to the corners. You may then alter the Taskbar and Navigation Properties: Right click an empty space on the taskbar and select properties: