Don't get me wrong, it's great that @calixteman wanted to implement that — JS should definitely be supported! I don't want to come off as rude or attacking.

For starters, JS reference specified in the [commit comment](https://github.com/mozilla/pdf.js/commit/8de98079ca05f8f7001ee077771055a57dc0e948) is outdated. It's version 8.1 from 2007… We're more than decade past that now. We should be implementing [Acrobat DC SDK](https://www.adobe.com/content/dam/acom/en/devnet/acrobat/pdfs/AcrobatDC_js_api_reference.pdf) ([here](https://help.adobe.com/en_US/acrobat/acrobat_dc_sdk/2015/HTMLHelp/#t=Acro12_MasterBook%2FJS_API_AcroJS%2FJavaScript_API.htm) in a nice HTML version).

Other than that, the Doc object now is only implemented with `info` property with standard fields (`Title`, `Author`, `Subject`, `Keywords`, `Creator`, `Producer`, `CreationDate`, `ModDate` and `Trapped`, case insensitive). But [according to the spec](https://www.adobe.com/content/dam/acom/en/devnet/acrobat/pdfs/AcrobatDC_js_api_reference.pdf#page=243) (even [in that old version](https://www.adobe.com/content/dam/acom/en/devnet/acrobat/pdfs/js_api_reference.pdf#page=243)), this object can contain other, non-standard properties, that can be set both in Acrobat interface and in JS (which are case-sensitive then).

Acrobat 9.0 introduced another field to that property, `Authors`, containing semicolon-delimited list of authors.

There are probably other problems with that code due to the outdated spec @calixteman was apparently working on.
this._numFields = 0;
    this._numPages = data.numPages || 1;
    this._pageNum = data.pageNum || 0;
    this._producer = data.Producer || "";
    this._subject = data.Subject || "";
    this._title = data.Title || "";
    this._URL = data.URL || "";
    
    
    this._info = new Proxy(
      {
        title: this.title,
        author: this.author,
        subject: this.subject,
        keywords: this.keywords,
        creator: this.creator,
        producer: this.producer,
        creationdate: this._creationDate,
        moddate: this._modDate,
        trapped: data.Trapped || "Unknown",
      },
      InfoProxyHandler
    );
    this._zoomType = ZoomType.none;
    this._zoom = data.zoom || 100;
    this._actions = createActionsMap(data.actions);
    this._globalEval = data.globalEval;
    this._pageActions = new Map();
  }
  _dispatchDocEvent(name) {