Create a zip file and download it

header("Content-type: application/zip"); 
header("Content-Disposition: attachment; filename=$archive_file_name");
header("Content-length: " . filesize($archive_file_name));
header("Pragma: no-cache"); 
header("Expires: 0"); 
readfile("$archive_file_name");

 <?php
$file_names = array('iMUST Operating Manual V1.3a.pdf','iMUST Product Information Sheet.pdf');

$zip = new ZipArchive;
$tmp_file = 'assets/myzip.zip';
    if ($zip->open($tmp_file,  ZipArchive::CREATE)) {
        $zip->addFile('folder/bootstrap.js', 'bootstrap.js');
        $zip->addFile('folder/bootstrap.min.js', 'bootstrap.min.js');
        $zip->close();
        echo 'Archive created!';
        header('Content-disposition: attachment; filename=files.zip');
        header('Content-type: application/zip');
        readfile($tmp_file);
   } else {
       echo 'Failed!';
   }

// http headers for zip downloads
header("Pragma: public");
header("Expires: 0");
header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
header("Cache-Control: public");
header("Content-Description: File Transfer");
header("Content-type: application/octet-stream");
header("Content-Disposition: attachment; filename=\"".$filename."\"");
header("Content-Transfer-Encoding: binary");
header("Content-Length: ".filesize($filepath.$filename));
ob_end_flush();
@readfile($filepath.$filename);

ob_clean();
flush();
readfile("$archive_file_name");

readfile("$archive_file_name");

Allowed memory size of 134217728 bytes exhausted (tried to allocate 292982784 bytes)

    $handle = fopen($zipPath, "rb");
    while (!feof($handle)){
        echo fread($handle, 8192);
    }
    fclose($handle);

foreach($file_names as $file)
{
    $inputFile = $file_path . $file;
    if (!file_exists($inputFile))
        trigger_error("The input file $inputFile does not exist", E_USER_ERROR);
    if (!is_readable($inputFile))
        trigger_error("The input file $inputFile exists, but has wrong permissions or ownership", E_USER_ERROR);
    if (!$zip->addFile($inputFile, $file))
        trigger_error("Could not add $inputFile to ZIP file", E_USER_ERROR);
}

$archive_file_name = $name.'iMUST_Products.zip';

$file_names = array('iMUST Operating Manual V1.3a.pdf', 'iMUST Product Information Sheet.pdf');

// $name should be declared before this line
$archive_file_name = $name.'iMUST_Products.zip';

//Download Files path
$file_path = $_SERVER['DOCUMENT_ROOT'].'/Harshal/files/';

zipFilesAndDownload($file_names, $archive_file_name, $file_path);

function zipFilesAndDownload($file_names, $archive_file_name, $file_path)
{

    $zip = new ZipArchive();
    // WE REUSED THE $file_path VARIABLE HERE THEN ADDED zipped FOLDER
    if ($zip->open($file_path.'zipped/'.$archive_file_name, ZIPARCHIVE::CREATE )!==TRUE) {
        exit('cannot open <'.$archive_file_name.'>');
    }
    //add each files of $file_name array to archive
    foreach($file_names as $files)
    {
        $zip->addFile($file_path.$files, $files);
    }
    $zip->close();
    //then send the headers to force download the zip file
    header("Content-type: application/zip"); 
    header("Content-Disposition: attachment; filename=$archive_file_name"); 
    header('Content-length: '.filesize($file_path.'zipped/'.$archive_file_name));
    header("Pragma: no-cache"); 
    header("Expires: 0"); 
    readfile("$archive_file_name");
    exit;
}

$archive_file_name = $file_path.'zipped/'.$name.'iMUST_Products.zip';