So it’s really weird. After messing with Krita for 3 hours trying to get the pen pressure to work, you have to initiate the windows 8+ pointer input that Nayo posted and then at the bottom right of your screen (in your taskbar next to the time and date), click the notifications “action center” button (it looks like a message). A side bar will pop up, click the “tablet mode” button that’s towards the bottom of the screen and you should now be able to use your pen with pen pressure in krita. Getting the pen to function efficiently the entire time without it dropping off mid-stroke is a whole other demon I’m trying to battle. 
Hopefully this helps. There’s little to no information out there for how to use the Yoga A940 with almost ANY application so there’s been quite a few headaches and growing pains with this computer.