Man, I stumbled into this exact rabbit hole a while back. You're looking for legitimate sources, and that's smart, because 'Daddy Crush' has that messy, wide distribution across a bunch of platforms.
For a straight PDF download, it's tricky. Most official romance publishers don't just hand out PDFs—they want you in their ecosystem. You might have luck on the publisher's own site if they offer direct sales, but I'd honestly start with Amazon. Buy the Kindle version and use Calibre with DeDRM tools to convert it; it's a bit of a process, but it's legal since you own the file. Some indie authors on Smashwords offer multiple formats including PDF right at purchase, so check if the author is selling there.
Otherwise, subscription services like Scribd sometimes let you download for offline reading in their app, but it's not a true PDF you own. Honestly, the hunt for a clean, legal PDF is half the struggle with these niche romance titles—often the easiest path is to buy the ebook and convert it yourself, which feels less shady than chasing random download links.