Still the Question mark problem - Page 1

Hi guys, I still having the question marks problem from half years ago...

this is what I have done:

$selection = "target.php";

ob_start();
include($selection);
$content = ob_get_clean();

echo "the following is dump:";
//echo $content; //commented from testing result mention below
var_dump($content);

throughout the echos,

I can see the content without errors
even var_dump contain all the codes
echo will just show the content, and the content is same and clean as the others

but the problem I'm still facing is that, if I use $content = "<page>...</page>"

var_dump still display string([number_of_char]) but didn't show on PDF, so I just don't know where this question mark comes from.

btw, var_dump present no difference no matter I use include of not.

I need to make the $selection variable so that I can make $_GET some parameter from different php with different parameter