Nobody wants PDFs. On desktop sites, it's common to add a (PDF Warning) to links that lead to PDFs.
And on a phone, PDFs are even worse. They're almost always sized for the desktop, which means you have to pinch and scroll to see anything, and I don't download stuff from Firefox often enough to know how to find and delete the menus for every single restaurant I eat at.
If the menu QR code led to a responsive website, I'd be fine with it. When the QR code leads to a PDF, it makes me angry. If the QR code led to an app I had to install, I'd walk directly out of the restaurant.