At the N4 level, you are expected to:

If you already have the PDF, print out the grammar and kanji sections. Use a physical pencil. Write every day. And for the love of Japanese, find the audio files for the listening section—otherwise, search "NHK Easy Japanese" for free, legal listening practice.

It is no secret that students often look for free PDF versions of textbooks to save money. A quick search for yields many results, but proceeding with caution is vital.