PHPExcel: the right way to open files

Just let PHPExcel figure out the file type by using PHPExcel_IOFactory::identify()

$filename = 'your_file.xls';

require_once 'PHPExcel/Classes/PHPExcel.php';

// Create new PHPExcel object
$filetype = PHPExcel_IOFactory::identify($filename);
$objReader = PHPExcel_IOFactory::createReader($filetype);
$objReader->setReadDataOnly(true);  // set this if you don't need to write
$objPHPExcel = $objReader->load($filename);

// go through each sheet
foreach ($objPHPExcel->getWorksheetIterator() as $worksheet) {
  ...
}