a straight legal PDF download of the 'Sword Art Online Progressive' light novels is a tough find. Yen Press, the English publisher, doesn't typically offer free PDFs; they sell digital editions. The best legal route is buying the ebooks from platforms like Amazon Kindle, Google Play Books, or Kobo. They sell the EPUB, not PDF, but reading apps handle that just fine. I know some people really want that specific PDF format for annotation or archiving, but converting an EPUB you own is usually the only way to get there legally.
Libraries are a great underrated option, too. If your local library uses Libby or OverDrive, you can borrow the digital editions for free, which is a perfect way to try before you buy. It's a bit of a dance—checking availability, waiting on holds—but it's completely above board. I'd steer clear of any site offering a full PDF for free; those are almost always unauthorized scans that don't support the author or publisher.
In the end, if you're a collector, buying the digital copies from the official stores is the most straightforward method. It gets you a clean, high-quality file immediately, and you know your money is going back to Reki Kawahara and the translators. The search for a ready-made PDF is often more trouble than it's worth, given how easy the purchase and conversion process can be.