@Override
    public void add(int id, Metadata metadata, InputStream is) throws IOException {
        super.add(id, metadata, is);
        docBytes.put(id, IOUtils.toByteArray(is));
    }
For now, this is an in-memory EmbeddedDocumentBytesHandler that stores
all the bytes in memory. Users can retrieve the documents with {@link #getDocument(int)}.

We'll need to make this cache to disk at some point if there are many bytes of
embedded documents.
tika-core/src/main/java/org/apache/tika/extractor/BasicEmbeddedDocumentBytesHandler.java