After two days of struggling this is the answer:
Microsoft Word encoding adds "\0" characters between all "real characters", so basically the word "hello" is actually "h\0e\0l\0l\0o\0".
The way to search inside the doc is:
$fileContent = file_get_contents($filePath);
$termArray = str_split($term);
$newTerm = '';
foreach ($termArray as $charTerm) {
$newTerm = $newTerm.$charTerm;
$newTerm = $newTerm."\0";
}
if (stripos($fileContent,$newTerm) !== false) {
// Term found in doc
}