Cf7 and fpdf - how to generate filenames by user and attach pdf to mail?

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FPDF

I am desperately trying to generate PDF files with user generated names by using data from cf7 form. The PDF files should send as attachement via cf7's mail function.

In makepdf.php first part is working. It generates files with names like LS-00019.pdf, LS18-12345.pdf and so on.
I am struggling with the second part. cf7 does not send the pdf file as attachement.

Thank you for your help!

What I have tried:

$fileName = 'LS18-' . $posted_data["lesernummer"] . '.pdf';
$pdf->Output(FPDF_PATH. $fileName, 'F'); 
add_filter( 'wpcf7_mail_components', 'mycustom_wpcf7_mail_components' );
function mycustom_wpcf7_mail_components($components){
if (empty($components['attachments'])) {
    $filepath = FPDF_PATH .$filename;
    $components['attachments'] = $filepath;
} 
return $components;
}