If you find a used Longman Grade 8 textbook for $15 on eBay or ThriftBooks, you can legally scan it for personal use (format shifting). Use a free scanning app like Microsoft Lens or Adobe Scan to create your own PDF from the chapters you need.
While not a PDF, Khan Academy covers every Grade 8 topic in order. You can print their worksheets (as PDFs) from the "Practice" section. It’s free, legal, and excellent. longman mathematics grade 8 pdf
Many international schools purchase institutional licenses for digital textbooks. Ask your school’s math department or librarian if they provide access to a school-wide Pearson account. Public libraries may also offer e-book lending through apps like OverDrive or Libby. If you find a used Longman Grade 8