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specified in the [commit comment](https://github.com/mozilla/pdf.js/commit/8de98079ca05f8f7001ee077771055a57dc0e948) is outdated.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There are probably other problems with that code due to the outdated spec @calixteman was apparently working on.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._fields.set(name, field);
    this._fieldNames.push(name);
    this._numFields++;
  }
  _getDate(date) {
    
    if (!date || date.length < 15 || !date.startsWith("D:")) {
      return date;
    }
    date = date.substring(2);
    const year = date.substring(0, 4);
    const month = date.substring(4, 6);
    const day = date.substring(6, 8);
    const hour = date.substring(8, 10);
    const minute = date.substring(10, 12);
    const o = date.charAt(12);
    let second, offsetPos;
    if (o === "Z" || o === "+" || o === "-") {
      second = "00";
      offsetPos = 12;
    } else {
      second = date.substring(12, 14);
      offsetPos = 14;
    }
    const offset = date.substring(offsetPos).replaceAll("'", "");
    return new Date(
      `${year}-${month}-${day}T${hour}:${minute}:${second}${offset}`
    );
  }
  get author() {