$link = 'https://google.com';

$unacceptables = array('https:','.doc','.pdf', '.jpg', '.jpeg', '.gif', '.bmp', '.png');

foreach ($unacceptables as $unacceptable)
{
        if (strpos($link, $unacceptable) === true) {

            echo 'Unacceptable Found<br />';

        }
         else {

            echo 'Acceptable!<br />';

        }
}

// ...
if (strpos($link, $unacceptable) !== false) {

if (strpos($link, $unacceptable) !== false) {