test.js

import React, { useRef, useEffect } from 'react';
import DocumentViewer from '@txtextcontrol/tx-react-document-viewer'

function App() {

  useEffect(() => {
    window.addEventListener('documentViewerLoaded', handleLoaded);
  }, []);

  const handleLoaded = (event) => {
    var xhr = new XMLHttpRequest();
    xhr.open("GET", "https://yourapi.domain.com/api/document", true);
    xhr.setRequestHeader("Access-Control-Allow-Origin", "*");
    xhr.send();

    xhr.onreadystatechange = function() {
      if (xhr.readyState == 4) {
        event.srcElement['TXDocumentViewer'].loadDocument(btoa(xhr.responseText), "loaded.html");
      }
    }
  };

  return (
    <DocumentViewer
      width="1000px"
      height="800px"
      basePath="https://backend.textcontrol.com?access-token=yourtoken">
    </DocumentViewer>
  );
}

export default App;