You can use this function, which creates a tempfile in the filesystem and returns the path to the downloaded file if everything worked fine:
function getFileContents($url)
{
// Workaround: Save temp file
$img = tempnam(sys_get_temp_dir(), 'pdf-');
$img .= '.' . pathinfo($url, PATHINFO_EXTENSION);
$fp = fopen($img, 'w+');
$ch = curl_init();
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0);
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_FILE, $fp);
curl_setopt($ch, CURLOPT_HEADER, false);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
$result = curl_exec($ch);
curl_close($ch);
fclose($fp);
return $result ? $img : false;
}