The series is famous for its "inductive" method—teaching through patterns and examples rather than heavy grammatical explanations in the main text. For the N4 level, the primary textbook used is , or sometimes the continuation from the Beginner Books 1 & 2 (depending on the edition and curriculum structure of the school).
Maybe you are struggling to find a clean PDF. Or maybe the layout isn't for you. Here are the top alternatives for N4 study that also have PDF/digital options. Minna No Nihongo N4 Pdf