$re = '/^Header 1$(?:\R(?!Header ).*+)*?\RNombre : Juan$(?:\R(?!Header ).*+)*/mi';
$str = 'Header 1
Codigo : c001
Nombre : Juan
Total : 45,78
Header 1
c001
Nombre : Juan
Cantidad : 23
Subtotal : 45.89
Total : 3410.67
Header 1
Codigo : c002
Nombre : Ana
Total : 45.89
Header 1
c001
Nombre : Juan
Cantidad:4';
preg_match_all($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