Lets say that I have some original DukeNukem sound files and I want to implement them into a sound board app: A) If I sell the app, is it fair use of the implentation of the sound files or will Duke Nukem's company ask me to (remove app/maybe sue me)? B) Then could I set the app as free in the AppStore so it can be classified as non-profit (one of the rules of the Copyright Act of 1976)? C) If B is possible, is it legal to have ads in the app or will that break the "non-profit" title? D) If any of the solutions above is allowable, does it matter if it on the iOS AppStore or the Mac AppStore? Here is the Copyright Act: "Copyright Disclaimer Under Section 107 of the Copyright Act 1976, allowance is made for "fair use" for purposes such as criticism, comment, news reporting, teaching, scholarship, and research. Fair use is a use permitted by copyright statute that might otherwise be infringing. Non-profit, educational or personal use tips the balance in favor of fair use."