I was looking for 'The Invisible Boy' just last week! From what I found, it's tricky to track down as a free PDF legally—most search results either link to shady sites or dead ends. The publisher usually keeps digital rights locked tight, so unless it's officially released as an ebook, you might have to settle for a physical copy or licensed digital purchase. I ended up borrowing it through my library's app, which was a lifesaver. Sometimes those niche titles pop up in unexpected places!
If you're dead set on a PDF, try checking academic databases or author/publisher websites—sometimes they offer sample chapters. But honestly, the tactile feel of flipping through a paperback adds to the charm of older novels like this one. I stumbled upon a used copy at a bookstore, and the yellowed pages gave it this weirdly nostalgic vibe.