How do I create a default association for files with an unknown extension?

A. Files with an unknown extension will bring up an "openwith" dialog when you double click on them however it is possible toassociate an application with files of an unknown type.

You can force this using the registry:

If you now double click on a file with no extension it will open with theapplication selected.

You can optionally delete the HKEY_CLASSES_ROOTUnknownshellopenas key andits content but it is not necessary and it will just remove the open withcontext menu option.

It is possible to just add a notepad option to the context menu of Unknown byusing the existing entry in HKEY_CLASSES_ROOT/Unknown/shell, adding a new keyvalue of NotePad and a new Key value of 'open' underneath Notepad then a new Keycalled 'command' under open. Set the (Default) value of command to Notepad.exe%1. Registry file to perform this:

REGEDIT4

[HKEY_CLASSES_ROOTUnknownshellotepad]

[HKEY_CLASSES_ROOTUnknownshellotepadopen]

[HKEY_CLASSES_ROOTUnknownshellotepadopencommand]
@="notepad %1"