Convert from PPT/PPTX to PDF

Hello, I want to create a service that accepts base64 ppt/pptx and will add a picture (png) there at the end and convert to pdf and send the base64 created pdf. I use LibreOffice and XMLSlideShow.

  1. When I create a file from base64 ppt/pptx, but an error occurs when opening it

    the code itself is like this
byte[] bytes = Base64.getDecoder().decode(base64);
     if (bytes != null) {
         try {
             FileDescriptor fileDescriptor = dataManager.create(FileDescriptor.class);
             fileDescriptor.setName(name + "." + type);
             fileDescriptor.setCreateDate(new Date());

             fileLoader.saveStream(fileDescriptor, () -> new ByteArrayInputStream(bytes));
             // сохраняем и присваиваем FileDescriptor
             fileDescriptor = dataManager.commit(fileDescriptor);
             NewEntity newEntity = metadata.create(NewEntity.class);
         } catch (FileStorageException e) {
             throw new RuntimeException(e);
  1. XMLSlideShow works with FileInputStream and filePath is needed for this. How can I get the filePath of the created pptx file?
    the sample code that I wrote (does not work)
 FileInputStream inputStream = new FileInputStream("http://localhost:8080/app/rest/v2/files/" + document.toUrlParam());
 XMLSlideShow  hslfSlideShow = new XMLSlideShow (inputStream);

document is a created FileDescriptor