Searching for a free PDF of "Architecting Solutions with SAP Business Technology Platform" usually leads to one of two things: the official handbook by Serdar Simsekler and Eric Du, or various community-contributed study guides and official overviews .
The book teaches the "clean core" paradigm. You will learn how to keep your SAP S/4HANA core pristine while extending functionality on BTP. This prevents upgrade bottlenecks and technical debt. Searching for a free PDF of "Architecting Solutions
For those looking for architectural guidance and downloadable PDF materials, these official and community resources are the most reliable: SAP BTP Guidance Framework Searching for a free PDF of "Architecting Solutions