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specified in the [commit comment](https://github.com/mozilla/pdf.js/commit/8de98079ca05f8f7001ee077771055a57dc0e948) is outdated.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There are probably other problems with that code due to the outdated spec @calixteman was apparently working on.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:about='61652fa7-fc1f-11dd-0000-ce81d41f9ecf' " +
      "xmlns:xap='http://ns.adobe.com/xap/1.0/' " +
      "xap:ModifyDate='2009-02-13T12:42:54+01:00' " +
      "xap:CreateDate='2009-02-13T12:42:54+01:00'>" +
      "<xap:CreatorTool>\\376\\377\\000P\\000D\\000F\\000C\\000r\\000e\\000a" +
      "\\000t\\000o\\000r\\000 \\000V\\000e\\000r\\000s\\000i\\000o\\000n" +
      "\\000 \\0000\\000.\\0009\\000.\\0006</xap:CreatorTool>" +
      "</rdf:Description><rdf:Description " +
      "rdf:about='61652fa7-fc1f-11dd-0000-ce81d41f9ecf' " +
      "xmlns:xapMM='http://ns.adobe.com/xap/1.0/mm/' " +
      "xapMM:DocumentID='61652fa7-fc1f-11dd-0000-ce81d41f9ecf'/>" +
      "<rdf:Description rdf:about='61652fa7-fc1f-11dd-0000-ce81d41f9ecf' " +
      "xmlns:dc='http://purl.org/dc/elements/1.1/' " +
      "dc:format='application/pdf'><dc:title><rdf:Alt>" +
      "<rdf:li xml:lang='x-default'>\\376\\377\\000L\\000&apos;\\000O\\000d" +
      "\\000i\\000s\\000s\\000e\\000e\\000 \\000t\\000h\\000\\351\\000m\\000a" +
      "\\000t\\000i\\000q\\000u\\000e\\000 \\000l\\000o\\000g\\000o\\000 " +
      "\\000O\\000d\\000i\\000s\\000s\\000\\351\\000\\351\\000 \\000-\\000 " +
      "\\000d\\000\\351\\000c\\000e\\000m\\000b\\000r\\000e\\000 \\0002\\0000" +
      "\\0000\\0008\\000.\\000p\\000u\\000b</rdf:li></rdf:Alt></dc:title>" +
      "<dc:creator><rdf:Seq><rdf:li>\\376\\377\\000O\\000D\\000I\\000S" +
      "</rdf:li></rdf:Seq></dc:creator></rdf:Description></rdf:RDF>" +
      "</x:xmpmeta>";
    const metadata = new Metadata(data);
    expect(metadata.has("dc:title")).toBeTruthy();
    expect(metadata.has("dc:qux")).toBeFalsy();
    expect(metadata.get("dc:title")).toEqual(
      "L'Odissee thématique logo Odisséé - décembre 2008.pub"
    );
    expect(metadata.get("dc:qux")).toEqual(null);