Man, that one's a bit tricky to pin down. Since 'Walking Disaster' is part of that 'Beautiful' series by Jamie McGuire, the PDF situation for individual chapters isn't as common as for whole books. You might have some luck on sites that host fan uploads, but those can be a real mess—watermarked pages, weird formatting, or missing sections altogether.
I tend to stick with the big ebook retailers for something this mainstream. Kindle, Kobo, or Google Play Books usually let you download the entire ebook as a PDF or EPUB after purchase, which is way more reliable than chasing down separate files. If you're set on reading chapter-by-chapter, the author's publisher might offer a sample with the first few chapters through their site, but a full chapter-by-chapter free PDF isn't really the standard model.
For free access, your local library's digital service, like Libby or OverDrive, is your most legit bet. You borrow the whole book for a couple weeks. It’s not a permanent PDF download, but it’s free and legal. I tried a few of those 'free PDF chapter' sites once and got more pop-up ads than actual reading done.