A code points, it does not carry

The most common misunderstanding about PDF QR codes is that the document is somehow stored inside the square. It is not. A QR code holds a small amount of text, typically a few hundred characters, so what it really carries is the address of your file. The phone reads that address, fetches the PDF and displays it. This is why a PDF code needs an internet connection while a WiFi or contact code does not.

Make the document phone-friendly

A PDF designed for A4 paper is punishing on a phone screen: the reader pinches, zooms and gives up. If the file exists mainly to be scanned from a poster or a leaflet, set it portrait, use a body size that stays legible at phone width, and keep it under a few megabytes so it loads on mobile data. Multi-column layouts and tiny footnotes are the usual culprits behind a document nobody reads.

Typical uses

Product manuals on packaging, care instructions on garment tags, spec sheets at trade stands, price lists in shop windows, safety data sheets on equipment, wine lists in restaurants, school newsletters, and property brochures on estate agent boards. In each case the printed thing stays small and cheap while the detail lives in a file you can revise whenever you want.

Use a dynamic code and that revision is free forever. Version two of the manual replaces version one behind the same link, and every unit already shipped points at the current document. You also see scan counts, which tell you whether anyone is reading the brochure you print by the thousand.