Last of 3 articles explains how macOS selects and starts the app with which to open a document which you double-clicked/tapped.
UTI
Second of 3 articles explains how macOS puts documents through its security checks before opening them.
How does macOS open the document that you double-click/tap? First of 3 parts explaining what should happen and where it can go wrong.
The moment you start writing apps that work with documents, you’ll need to know how to use UTIs. That requires inspired searching, guesswork, and trial and error.
Additional information is now shown for UTIs, it has its own custom app icon, and works wonderfully in Dark Mode.
What to do when you need to use Uniform Type Identifiers, only to discover that Apple’s reference manual hasn’t been updated for nearly 9 years: write an app!
The Desktop and Finder illusions are held together by Launch Services, which associates file types with apps. This and more now hinge on the UTI.
The Eclectic Light Company 