What is the most annoying part of sharing PDFs or files by link?

I am launching LinkInSeconds soon and would love to learn from people here.

The idea is simple: upload a PDF, image, or HTML page and get a clean shareable link with QR code and basic view analytics. Viewers do not need to install anything or create an account.

I started this because normal file sharing can feel messy sometimes: permission issues, expired links, or no idea if someone opened the file.

Curious to know: when you share files with clients, friends, or teams, what is the most annoying part for you?