The Kursbuch teaches you the concepts. The (workbook) drills them. You need both. The official PDF bundle often includes the workbook for a slight discount. Never study the Kursbuch alone.
Publishing a textbook is incredibly expensive (authors, illustrators, audio engineers, editors). Downloading a pirated PDF denies the creators their income. Furthermore, many pirated PDFs are low-quality, missing pages, or watermarked. netzwerk a1 kursbuch pdf
Even if you ignore the legal issues, pirated PDFs are often terrible: The Kursbuch teaches you the concepts