After updating to CC 2015, I am no longer able to drag pdf files into PS documents. When attempting to do so, it locks up PS and my system and I have to do a hard reboot because PS will not force quit. I've been dragging pdfs into PS docs for many years, so this is a new one on me.
If an application freezes, you can force quit that application - there should be no need for a system reboot.
Anything that freezes the full system and forces a reboot means it is happening at the OS level: an OS bug, a low level driver bug, or hardware failure. Applications cannot freeze the entire system.