That's normal if you recieve levels through hotmail. Make them send as a ZIP nextime though. Do what KJ said (Rename the file to NW)..
I open NW files as text documents; it's easier to check if there is any stolen / abusive scripts in the level before you upload, I suggest you all do that too
(At the bottom of the text document it shows the scripts / signs in the level)
It's not ASCII, It's the graal tile formations (Each tile number)..