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specified in the [commit comment](https://github.com/mozilla/pdf.js/commit/8de98079ca05f8f7001ee077771055a57dc0e948) is outdated.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There are probably other problems with that code due to the outdated spec @calixteman was apparently working on.
'</rdf:Description></rdf:RDF></x:xmpmeta><?xpacket end="w"?>';
    const metadata = new Metadata(data);
    expect(metadata.has("dc:title")).toBeTruthy();
    expect(metadata.has("dc:qux")).toBeFalsy();
    expect(metadata.get("dc:title")).toEqual("");
    expect(metadata.get("dc:qux")).toEqual(null);
    expect(metadata.getAll()).toEqual({
      "dc:creator": "",
      "dc:description": "",
      "dc:format": "application/pdf",
      "dc:subject": "",
      "dc:title": "",
      "pdf:keywords": "",
      "pdf:pdfversion": "1.7",
      "pdf:producer": "PDFKit.NET 4.0.102.0",
      "xap:createdate": "2018-12-27T13:50:36-08:00",
      "xap:creatortool": "",
      "xap:metadatadate": "2018-12-27T13:50:38-08:00",
      "xap:modifydate": "2018-12-27T13:50:38-08:00",
    });
  });
  it('should correctly handle metadata containing "&apos" (issue 10407)', function () {
    const data =
      "<x:xmpmeta xmlns:x='adobe:ns:meta/'>" +
      "<rdf:RDF xmlns:rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#'>" +
      "<rdf:Description xmlns:dc='http://purl.org/dc/elements/1.1/'>" +
      "<dc:title><rdf:Alt>" +
      '<rdf:li xml:lang="x-default">&apos;Foo bar baz&apos;</rdf:li>' +
      "</rdf:Alt></dc:title></rdf:Description></rdf:RDF></x:xmpmeta>";
    const metadata = new Metadata(data);