A menu QR code is simply a link to a web page or a hosted PDF that contains your menu. Guests scan it, the menu opens in the browser, and nobody has to hand out, wipe down or reprint a physical card between sittings. The important detail is that the code points to a URL you control, so when you swap in a seasonal menu, add allergen notes or change a price, you edit the page - not the hundreds of stickers already stuck to your tables.
If you can, use a lightweight HTML menu page rather than a PDF. It loads faster on a phone, reflows to fit the screen instead of forcing guests to pinch and zoom, is easier for screen readers, and can be indexed by search engines so people find your dishes before they walk in. A PDF works, but treat it as a fallback.
Generate one master code for the whole menu and place it consistently - table tents, a sticker on the corner of each table, the front window, and the receipt. Use a dark code on a light background with a generous empty margin, because restaurant lighting is often warm and dim, which is the hardest condition for a phone camera to read a low-contrast code.