Application associated with a specific file name extension

To determine which application is associated with a specific file name extension you can look in the registry under HKEY_CLASSES_ROOT.

Easier is to use the Windows API function FindExecutable() - see the following example.
The code shows the fully qualified associated application or the last error (using GetLastError).

	program Project1; uses Forms, Dialogs, ShellAPI, SysUtils, Windows; {$R *.RES} var sApp : array [0..256] of char; begin // this should return something like c:\program files\office\excel.exe if FindExecutable('c:\temp\xxx.xls', nil, sApp) >= 32 then ShowMessage(sApp) else ShowMessage(SysErrorMessage(GetLastError)); end.