uses

  ..., ShellAPI;

function MrsGetFileType( const strFilename: string ): string;

var

  FileInfo: TSHFileInfo;

begin

   FillChar( FileInfo, SizeOf( FileInfo), #0 );

   SHGetFileInfo( PChar( strFilename), 0, FileInfo, SizeOf( FileInfo ), SHGFI_TYPENAME );

   Result := FileInfo.szTypeName;

end;

procedure TForm1.Button1Click(Sender: TObject);

begin

   Caption := MrsGetFileType( 'c:\autoexec.bat' );

end;