Attach (recommended) or Link to PDF file here:  [test.pdf](https://akmer.aikucun.com/a94a8fe5ccb19ba61c4c0873d391e987982fbbd3_1616477914120_83.pdf)


Configuration:
- Web browser and its version: chrome 87.0.4280.88
- Operating system and its version: windows10
- PDF.js version: 2.6.347
- Is a browser extension:

Steps to reproduce the problem:
1. just open 

What is the expected behavior? (add screenshot)

What went wrong? (add screenshot)
![image](https://user-images.githubusercontent.com/17724610/112087066-473f8f80-8bc8-11eb-8efb-56139ec42a9c.png)

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):

if (dict.has("UF")) {
      return dict.get("UF");
    } else if (dict.has("F")) {
      return dict.get("F");
    } else if (dict.has("Unix")) {
      return dict.get("Unix");
    } else if (dict.has("Mac")) {
      return dict.get("Mac");
    } else if (dict.has("DOS")) {
      return dict.get("DOS");
    }
    return null;
  }
  FileSpec.prototype = {
    get filename() {
      if (!this._filename && this.root) {
        var filename = pickPlatformItem(this.root) || "unnamed";
        this._filename = stringToPDFString(filename)
          .replace(/\\\\/g, "\\")
          .replace(/\\\//g, "/")
          .replace(/\\/g, "/");
      }
      return this._filename;
    },
    get content() {