The prebuilt files include `web/pdf_viewer.js` with some viewer APIs. Those are missing from type declarations.
let reason = process.env.PDFJS_UPDATE_REASON;
    
    if (typeof reason === "string") {
      const reasonParts =
        /^(See )(mozilla\/pdf\.js)@tags\/(v\d+\.\d+\.\d+)\s*$/.exec(reason);
      if (reasonParts) {
        reason =
          reasonParts[1] +
          "https://github.com/" +
          reasonParts[2] +
          "/releases/tag/" +
          reasonParts[3];
      }
    }
    const message =
      "PDF.js version " + VERSION + (reason ? " - " + reason : "");
    safeSpawnSync("git", ["add", "*"], { cwd: DIST_DIR });
    safeSpawnSync("git", ["commit", "-am", message], { cwd: DIST_DIR });
    safeSpawnSync("git", ["tag", "-a", "v" + VERSION, "-m", message], {
      cwd: DIST_DIR,
    });
    console.log();
    console.log("Done. Push with");
    console.log(
      "  cd " + DIST_DIR + "; git push --tags " + DIST_REPO_URL + " master"
    );
    console.log();
    done();
  })
);