PHP ZipArchive, how to increase compression rate?

I'm using PHP ZipArchive for compressing folder in PHP.

The files and the subfolders are well added to the archive, but I would like to know how to increase the compression level of the archive.

The following code is based on the exemple of this commit : https://github.com/php/php-src/commit/3a55ea02

$zip = new ZipArchive();
$filename = "output/a.zip";

if (!$zip->open($filename, ZIPARCHIVE::CREATE | ZipArchive::OVERWRITE)) {
    exit("cannot open <$filename>\n");
}

$zip->addFromString("testfilephp.txt", "#1 This is a test string added as testfilephp.txt.\n");
$zip->addFile('output/done/monday/pdftest.pdf', 'test.pdf');

$zip->setCompressionName("test.pdf", ZipArchive::CM_DEFLATE, 6);
$zip->setCompressionIndex(2, ZipArchive::CM_DEFLATE, 6);

$zip->close();
Copy code

The compression is not enougth.

• Archive weight : 7 690 288 bytes
• PDF File"output/done/monday/pdftest.pdf" weight : 7 809 870 bytes

For this exemple, I would like that the archive weight be less than 5 000 000 bytes.

Is any anyone hase a solution for define a real compression level ?

Thanks by advance for your help and have a good week.

MickaГ«l

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