Keep the code conventional
Use dark modules on a light background, preserve the square finder patterns, and keep decoration outside the code. The sign around it can carry the visual personality.
Respect the margin
Keep at least four blank modules around the symbol. Do not let text, a border, a logo, or a printer crop mark enter this quiet zone.
Export for the real size
A print-ready PDF should describe the intended physical page—not a screenshot stretched by a print dialog. Select Actual size or 100% unless your printer workflow specifically requires scaling.
Watch material and finish
Wrinkles, curved containers, metallic stock, glare, and low contrast can defeat an otherwise valid code. Test the intended paper and finish.
Run the final proof
Scan the exported file, print one sample at actual size, test several phones, and confirm the destination one last time before ordering a large run.
Sources
Primary references used for factual guidance: