Always check the file’s metadata or the first page for the edition number (e.g., “Second Edition” or “Third Edition” with a 2020 copyright date). American English File 3 is currently in its 3rd edition (released 2021). Many free PDFs are for the 2nd edition (released 2013), which is significantly different.
Open the answer key PDF. Mark correct answers with a check (✓) and wrong ones with an X using a red pen or digital annotation tool. American English File 3 Workbook Answer Key Pdf