var

    Reg: TRegistry;

    FileExt:String;

    FileType:String;

    MIMEType:String;

    ExecName:String;

begin

    FileExt:='.test';

    FileType:='Test File';

    MIMETYPE:='text/plain';

    ExecName:=Application.ExeName +' %1';

    if ParamCount>0 then

    begin

        self.Memo1.Lines.LoadFromFile(ParamStr(1));

    end

    else

    begin

        Reg := TRegistry.Create;

        Reg.RootKey :=HKEY_CLASSES_ROOT;

        Reg.OpenKey(FileExt, True);

        Reg.WriteString('', FileType);

        Reg.WriteString('Content Type', MIMEType);

        Reg.OpenKey('shell\open\command',True);

        Reg.WriteString('', ExecName);

        Reg.CloseKey;

        Reg.Free;

    end;

end;