I was actually just hunting for this myself a few weeks ago! My local library's digital catalog didn't have it, which was a bummer. I did find a few sample pages on the publisher's official site, Scholastic I think, but it was really just a couple of interior panels—enough to get a feel for the art style, but not a full chapter.
What worked for me was checking the major ebook retailers. Sites like Amazon, Google Play Books, and Apple Books usually let you download a sample. I grabbed the Kindle sample, and it gave me the first twenty-something pages. It's not labeled as 'chapter one' explicitly, but it covers a decent chunk of the beginning, up to when Bella first sees Edward in the cafeteria. The image quality in the PDF sample was crisp, no watermarks or anything. It's a solid way to see if you like the adaptation before committing.
Honestly, a full free chapter in PDF floating around seems unlikely through official channels. The whole point of the sample is to give you a taste, not the whole meal. I'd stick with the retailer previews; they're legit and the easiest bet.