Hi. I had the same problem. I was using a Mac and when I downloaded my K-1, it came as a txf.txt file. I was unable to import it into Turbotax. 

Here is what I did:

I downloaded the K-1 on a PC (it downloaded as a .txf). Then I emailed that file to myself and got it on my Mac. I was then able to import it in Turbotax on the Mac. 

I hope this helps!