While there is no single "official" free PDF hosted by the author, you can access verified digital copies of William Zinsser's Writing to Learn through legitimate library and educational platforms: Where to Find Verified Copies Internet Archive
William Zinsser ’s Writing to Learn argues that writing is not just a way to record what you know, but a tool for what you know. He advocates for "writing across the curriculum," meaning that everyone—from mathematicians to chemists—should use writing to organize their thoughts and clarify complex ideas. A Piece of "Writing to Learn" writing to learn william zinsser pdf verified