I have Unity Free and my friend have Unity Pro (Legit version), and he agreed to share me some of the Unity Pro script to write into my Unity Free (like copy/paste), is it illegal if I use those script in my game ?, cause I didn’t pat money for it.
There’s no such thing as a “Unity Pro” script, so it’s not illegal 
If it’s a script that makes use of features only available in Unity Pro (say, rendertextures, off-mesh navlinks, full screen effects etc) those features will simply not work when you try to run the script.