How to use "doable"? And is that common?

Question

Answer

Pretty common in casual language. To express that something is possible but there might be a downside.
She wants me to buy everything on the list and then pick up Johnny when school gets out. I don’t think it’s doable.

Can you pick up Dad on the way over? 
It’s doable. (I can)
It’s doable but we’ll be a little late then. (I can but ...)

Answer

Yes "doable" is commonly used. 
e.g.
 Yes, I do think it's doable to learn Japanese in 3 years.
No, it's just not doable. We cannot issue a refund for a product you bought 1 year ago.