PNGをPNGにマージするNode API

import * as fs from "fs";

// 現在の API は開発中です。
const wordsApi = new WordsApi("####-####-####-####-####", "##################");

const document = fs.createReadStream("Input1.png");
const mergeProps = new model.ImageEntry({
    fileReference: model.FileReference.fromRemoteFilePath("Input2.png")
})
const imageEntries = [
    mergeProps
]
const imageList = new model.ImageEntryList({
    imageEntries: imageEntries
})
const appendDocumentOnline = new model.AppendDocumentOnlineRequest({
    document: document,
    imageList: imageList
});

wordsApi.appendDocumentOnline(appendDocumentOnline)
.then((appendDocumentOnlineResult) => {
    console.log("Result of AppendDocumentOnline: ", appendDocumentOnlineResult);

    const convertDocument = new model.ConvertDocumentRequest({
        document: appendDocumentOnlineResult,
        format: "png"
    });

    wordsApi.convertDocument(convertDocument)
    .then((convertDocumentResult) => {
        console.log("Result of ConvertDocument: ", convertDocumentResult);
    });
});