A PDF or on-screen proof shows layout and approximate color. It does not show exactly how the job will look on press and on the actual substrate. Relying on it for color-critical work leads to mismatch.
Why digital and print differ
Monitors are RGB and emit light; print is CMYK on paper or vinyl and reflects light. Substrate color, texture, and finish change the look. The same file on different papers will look different. A screen cannot show that.
When to get a hard proof
When color or brand match is critical, or when it is a first run with a new vendor, request a printed proof. It may add cost and time but it is the only way to confirm how the job will look.
Before you approve digitally
• Confirm you are okay with approximate color and substrate difference.
• For critical color, request a hard proof or accept the risk.
• Understand that "approved" means we run to that proof; screen approval is still approval.
Common mistake
Approving a PDF and then being surprised that the print does not match your monitor. It never will exactly. For match-critical work, get a hard proof.