```php

// You can also add an attachment to the PDF as an stream (string). The conditions are the same as above for the attachAdditionalFileByRealFile method
// The only difference to attachAdditionalFileByRealFile is that the attachAdditionalFileByContent method accepts 4 parameters, whereby here (as with attachAdditionalFileByRealFile)
// the last two can be omitted. You only need to specify a file name under which the file is to be embedded

$zugferdDocumentPdfBuilder = ZugferdDocumentPdfBuilder::fromPdfFile($zugferdDocumentBuilder, '/tmp/existingprintlayout.pdf');
$zugferdDocumentPdfBuilder->attachAdditionalFileByContent('<xml>....</xml>', 'additionalDocument.csv', "Some other display Name", ZugferdDocumentPdfBuilderAbstract::AF_RELATIONSHIP_SUPPLEMENT);
$zugferdDocumentPdfBuilder->generateDocument();
$zugferdDocumentPdfBuilder->saveDocument('/tmp/merged.pdf');

```