$re = '/[a-z]{3}_(ANEXO|(A|a)nexo)_[A-Za-z]{1,7}_[A-Z]{1}_[A-Z0-9]{2,5}...\.pdf/';
$str = 'dge_ANEXO_II_F_TJ[1].pdf
dge_anexo_II_F_TJ[1].pdf
dge_Anexo_II_F_TJ[1].pdf
dge_aNEXO_II_F_TJ[1].pdf
dge_AneXo_II_F_TJ[1].pdf
dGe_AneXo_II_F_TJ[1].pdf // Erro "G"
dge_AneXo_Ii_j_TJ[1].pdf // Erro "j"
dge_AneXo_II_F_Tr[1].pdf // Erro "r"
dge_AneXo_II_F_TJ[TT].pdf // Erro "TT"
';
preg_match_all($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