The plain-English version
An operating-system relationship that lets an app participate in opening a supported file type.
Why it matters
It affects launch arguments and how documents enter the application.
Let’s make it click
Opening a custom note file can activate the app with that file’s path.
Vibe Bro’s heads-up
Treat an externally supplied path as input to validate rather than assuming every associated file is trustworthy.
The docs behind it
Documentation links checked .
Editorial review · October 28, 2026
Supported: Microsoft documents registration and activation when a chosen default handler opens a file, including validation of untrusted contents.