When user register a application by user choice, there are some registry entries automatically created by windows. By doing the same behaviors like windows, application can be launched automatically by clicking associated files.

uses System.Win.Registry;

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Procedure TForm1.FormCreate(Sender: TObject);
begin
  with TRegistry.Create do
    try
      RootKey := HKEY_CURRENT_USER;
      if OpenKey('Software\Classes\.kes', true) then begin
        WriteString('', '.kes_auto_file');
      end;
    finally
      Free;
    end;

  with TRegistry.Create do
    try
      RootKey := HKEY_CURRENT_USER;
      if OpenKey('Software\Classes\.kes_auto_file\shell\open\command', true) then begin
        WriteString('', '"' + ParamStr(0) + '" "%1"');
      end;
    finally
      Free;
    end;

  with TRegistry.Create do
    try
      RootKey := HKEY_CURRENT_USER;
      if OpenKey('Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.kes\UserChoice', true) then begin
        WriteString('', 'Applications\EmployeeSurvey.exe');
        WriteString('ProgId', '.kes_auto_file');
      end;
    finally
      Free;
    end;
end;