That's just asking for trouble.
Just like Google's cache is?
Just like Google's cache is?
Also, scribd show ads right next to every content that they don't own.
The real issue is where the content comes from. The browser doesn't provide a document - it's a dumb conduit for the page you're after. Whether you paid for your browser (Windows) or it's ad supported is irrelevant since it is itself incapable of copyright infringement. This isn't true of Scribd.
Why not? It's a PDF reader that you pay to use by looking at ads.