The prebuilt files include `web/pdf_viewer.js` with some viewer APIs. Those are missing from type declarations.
const plugins = [];
  if (!disableLicenseHeader) {
    plugins.push(
      new webpack2.BannerPlugin({ banner: licenseHeaderLibre, raw: true })
    );
  }
  
  output.globalObject = "this";
  return {
    mode: "none",
    output,
    performance: {
      hints: false, 
    },
    plugins,
    resolve: {
      alias: {
        pdfjs: path.join(__dirname, "src"),
        "pdfjs-web": path.join(__dirname, "web"),
        "pdfjs-lib": path.join(__dirname, "web/pdfjs"),
      },
    },
    devtool: enableSourceMaps ? "source-map" : undefined,
    module: {
      rules: [
        {
          loader: "babel-loader",
          exclude: babelExcludeRegExp,
          options: {
            presets: skipBabel ? undefined : ["@babel/preset-env"],