Windows – Where in the registry does Windows store with which program to open certain file types

windowswindows 7windows xpwindows-registrywindows-vista

After installing Adobe PDF reader, it opens files with the .PDF file extension. Ones' default web browser opens .html files and notepad opens .txt files, etc.

Where exactly in the registry are these filetype – program associations stored in the registry?

In other words, how does Windows know with which software/program it must open a certain file(type)?

Best Answer

The open with associations are all stored in HKEY_CLASSES_ROOT.

This is a special registry hive that combines the local user's associations in HKEY_CURRENT_USER\Software\Classes with the system's associations in HKEY_LOCAL_MACHINE\Software\Classes.

Here's a shot from my registry for the PDF association you mention in your question:

PDF file association in the registry

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