Don't hoard PDFs. Do past papers.
Having a PDF on your phone is great for revising definitions (e.g., "What is magnetic flux?"), but DSE Physics Paper 1A and 1B are about calculation and application. You cannot practice vector addition or circuit analysis by scrolling a PDF. dse physics textbook pdf
The Hong Kong Public Library (HKPL) offers e-books. While they may not have the latest edition of every textbook, they do have reference books and past paper solutions available for free loan as PDFs via the HyRead or SUEP apps. Don't hoard PDFs
?** Here is the hard truth: Physics is not a reading subject. "What is magnetic flux?")