How do I download a file which is not URL in React Native?

Question

It's a html file which is generated by template and converted to pdf. I've tried using blob and fetch only accept http/https.

let options = {
  html: genHtmlString(rcpt, rcptTemp['pay']),
  fileName: 'Pay' + rcptObj['ref'],
  directory: 'Documents',
  base64: true,
  addAndroidDownloads: {
    useDownloadManager: true,
    notification: true,
    description: 'Downloading File',
  },
};
let file = await RNHTMLtoPDF.convert(options);