$re = '/(?<=signature date\.\r?\n)\w+(?=\sSignatory attests)/m';
$str = 'to execute Form 4506-C on behalf of the taxpayer. Note: This form must be received by IRS within 120 days of the signature date.
Signatory attests that he/she has read the attestation clause and unon so reading declares that he/she has the authority to sign the
Form 4506-C. See instructions.
to execute Form 4506-C on behalf of the taxpayer. Note: This form must be received by IRS within 120 days of the signature date.
X Signatory attests that he/she has read the attestation clause and unon so reading declares that he/she has the authority to sign the
Form 4506-C. See instructions.
to execute Form 4506-C on behalf of the taxpayer. Note: This form must be received by IRS within 120 days of the signature date.
asdas Signatory attests that he/she has read the attestation clause and unon so reading declares that he/she has the authority to sign the
Form 4506-C. See instructions.
';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php