PDFTK on plesk (centos) – Stack Overflow

I’m trying to use PDFTK on a php page hosted on a PLESK server (Centos) but I have an error…

PDFTK was successfully installed with composer

If I use :

$pdf = new Pdf('form.pdf');
$result = $pdf->fillForm([
    'name'=>'test name',
    'email' => 'test email',
])
->needAppearances()
->saveAs('form_filled.pdf');

I have this error:

sh: pdftk: command not found

I think I found an idea in the documentation :
With Plesk (onCentos), I think you need to indicate the full path of pdftk, but I don’t know how to find it…

$pdf = new Pdf('/path/my.pdf', [
    'command' => '/some/other/path/to/pdftk',
    // or on most Windows systems:
    // 'command' => 'C:\Program Files (x86)\PDFtk\bin\pdftk.exe',
    'useExec' => true,  // May help on Windows systems if execution fails
]);

Could someone help me or have another idea… Thank you