The answer lies in edge cases and trust. Only Adobe Reader guarantees perfect rendering of PDF/X (for printing), PDF/A (for archiving), and PDF/E (for engineering). Only Adobe Reader reliably executes complex JavaScript within forms. And only Adobe Reader offers the full suite of commenting, measuring, and accessibility tools (screen reader integration) without compromise. The download persists because the PDF is not just a "picture of a document"; it is an active container, and Adobe holds the master key.