"A free PDF from 2021 is the same as the official Fourth Edition." Reality: IIBA released minor errata and clarifications in 2022 and 2023. The official PDF includes these updates. Free versions usually do not.
"Business Analysis" fourth edition is a thorough and practical guide that covers the key concepts, techniques, and best practices of business analysis. The book provides a clear and concise overview of the business analysis process, including requirements gathering, analysis, and solution implementation.