PDFs are where AI gets sloppy. So they're the best place to learn the checking moves.

Hand an AI a spreadsheet and it counts. Hand it a long PDF and it summarizes, quotes, and now and then fills a gap from memory without telling you. Ask around and you'll meet people who got two different answers from the same document. That's not a rumor, it's the ordinary experience, and it's the reason this lesson exists.

You're about to learn the two moves that fix it, on a document of your own: make it show its pages, and ask a second tool the same question. When you leave, an answer about a PDF will come with its pages attached and a second opinion on file.