CURL - хороший путь:
$toSearch = 'Questions';
// create curl resource
$ch = curl_init();
// set url
curl_setopt($ch, CURLOPT_URL, "http://stackoverflow.com/");
//return the transfer as a string
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
// $output contains the output string
$output = curl_exec($ch);
// close curl resource to free up system resources
curl_close($ch);
//search for the string
if(strpos($output, $toSearch ) !== FALSE ) {
echo "Found The Word " . $toSearch;
}