Why can't I use my downloaded music as ringtones?

[AC Question]

All of the downloaded (purchased through Amazon) music I have on my phone have little lock icons next to them & won't allow me to use them as ringtones. I've never had this issue before. Is there a way to 'unlock' them??

 

[B. Diddy]

Welcome to Android Central! Where do you see the lock icons -- in a file manager app? What directory are the files located in?