...
my $user = $mydb::Config::odbc_def->{ $db } { user };
my $pass = $mydb::Config::odbc_def->{ $db } { pass };
$dbh = DBI->connect("DBI:ODBC:$db",$user, $pass, {RaiseError => 1});

# Insert pdf file attached with the reference number.

my $sql="UPDATE main SET pdf='$pdf_file[0]' WHERE number='$number' AND ref='$ref'";
      $sth = $dbh->prepare($sql);
      $sth->execute() || die $sth->errstr;
      $dbh->disconnect or warn "Disconnection failed: $DBI::errstr\n";