$stack = array("par1","par2", "par3","par4");

foreach ($stack as $prof){
    echo $prof , '<br>';
    $url = "http://www.myservice.eu";
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($ch, CURLOPT_POST, true);
    curl_setopt($ch, CURLOPT_POSTFIELDS, $prof);
    $output = curl_exec($ch);

    $jsonDecode =json_decode($output);
    echo "value is ".$jsonDecode -> field1."<br>";

    curl_close($ch);
    echo "<br><br>";
}

$stack = array("search=par1","search=par2","search=par3");

$filename = "test.txt";
$source_file = fopen( $filename, "r" ) or die("Couldn't open $filename");
while (!feof($source_file)) {

    array_push($stack, "search=".fgets($source_file));
}
fclose($source_file);