Amazon, VitalSource, and Google Play Books often sell official eBook versions of Oxford IB English B or Pearson Baccalaureate for roughly half the price of the physical book. You can read these on any device without the guilt of piracy.
Your PDF will likely be divided into the five core themes. Do not read the book front-to-back. ib english b textbook pdf
Here is a study plan using your digital textbook: Amazon, VitalSource, and Google Play Books often sell
A high-quality IB English B textbook is structured around these themes. It provides the vocabulary lists, reading comprehension exercises, and listening samples necessary to master the syllabus. If you download a PDF that does not reference these themes explicitly, it is likely outdated (pre-2018 curriculum) and will not adequately prepare you for the current exams. Do not read the book front-to-back
If no to any of these, delete the file. It is worse than useless—it is misleading.