Is Apache FOP thread-safe for different documents

I am deveveloping a Spring Boot - application which should convert XML to PDF by using XSLT. I would like to use Apache FOP, but it states in its own documentation (https://xmlgraphics.apache.org/fop/2.6/embedding.html)

Apache FOP may currently not be completely thread safe. The code has not been fully tested for multi-threading issues, yet.

Unfortunately the docs don't tell what exactly is not tested yet. Is it possible to convert several independent XMLs into several independent PDFs in paralell (with multiple CPU cores)?

private URI convertToPDF(byte[] body, byte[] xsl, String pdfFileName) throws Exception {
    File pdfFile = new File(saveDirectory, pdfFileName);
    FOUserAgent foUserAgent = fopFactory.newFOUserAgent();
    // Setup output
    try(BufferedOutputStream out = new BufferedOutputStream(new FileOutputStream(pdfFile));) {
        // Construct fop with desired output format
        Fop fop = fopFactory.newFop(MimeConstants.MIME_PDF, foUserAgent, out);

        // Setup XSLT
        TransformerFactory factory = TransformerFactory.newInstance();
        Transformer transformer = factory.newTransformer(new StreamSource(new ByteArrayInputStream(xsl)));

        // Setup input for XSLT transformation
        Source src = new StreamSource(new ByteArrayInputStream(body));

        // Resulting SAX events (the generated FO) must be piped through to FOP
        Result res = new SAXResult(fop.getDefaultHandler());

        // Start XSLT transformation and FOP processing
        transformer.transform(src, res);
        
        return pdfFile.toURI();
    }
}

    Configuration
    public class ConverterConfig {
        @Bean
        public FopFactory fopFactory() {
          return FopFactory.newInstance(new File(".").toURI());
        }
    }