Thanks for perfect answer. I also found it is an OFL license in installed font setting window. Thank you so much.

Hi, I am new in dafont. Wish to use a font [Aurulent Sans] from Stephen G. Hartke. because the license classification is Public Domain / GPL / OFL. So I am confuse which rule to follow. want to contact Mr Hartke but no e-mail information too. May I know what rule to follow when is "Public Domain / GPL / OFL"?