First of all, I'd be careful looking for a direct PDF download of 'Fat Keily'. I haven't come across a published book with that exact title from a major publisher, so it's likely a self-published or web novel. That changes the landscape quite a bit. My main piece of advice is to be extremely wary of any site offering a 'free PDF download' of a full, contemporary book. Those are almost always pirate sites, and they're riddled with malware, intrusive ads, and sometimes files that aren't even the right book.
For works that might originate on platforms like Wattpad or Royal Road, the author sometimes makes PDFs available for free or for a small fee on their own personal site or a platform like Ko-fi as a thank you to supporters. Your absolute safest bet is to search for the author's name directly. See if they have a social media link or a blog where they might host their work legitimately. I've found a few indie authors that way.
Failing that, check if the story is serialized on a legitimate reading app or website. Sometimes you can read the entire thing for free, chapter by chapter, with ads, which supports the creator in a small way. Downloading a pirated copy from a random forum link does nothing for the author and puts your device at risk. It's just not worth the hassle for a potentially corrupted file or a story that might be incomplete.