Hello!

Let me know if i should have opened this issue on the [pdfjs-dist](https://github.com/mozilla/pdfjs-dist) repo but I though here would fit.

I'm using pdfjs-dist and I'm in need of some more types to be exported. I have no idea how the types end up in the dist-repo but would love to open a PR if only someone could point me in the right direction 😃 Since I was using an older version of pdfjs-dist I realize the only type I need that's not in the type defs in the latest release are _PageViewport_ from _[display/display_utils](https://github.com/mozilla/pdf.js/blob/master/src/display/display_utils.js#L153)_.
expect(
        worker1.port !== worker2.port &&
          worker1.port !== worker3.port &&
          worker2.port !== worker3.port
      ).toEqual(true);
      worker1.destroy();
      worker2.destroy();
      worker3.destroy();
    });
    it("gets current workerSrc", function () {
      if (isNodeJS) {
        pending("Worker is not supported in Node.js.");
      }
      const workerSrc = PDFWorker.workerSrc;
      expect(typeof workerSrc).toEqual("string");
      expect(workerSrc).toEqual(GlobalWorkerOptions.workerSrc);
    });
  });
  describe("PDFDocument", function () {
    let pdfLoadingTask, pdfDocument;
    beforeAll(async function () {
      pdfLoadingTask = getDocument(basicApiGetDocumentParams);
      pdfDocument = await pdfLoadingTask.promise;
    });
    afterAll(async function () {
      await pdfLoadingTask.destroy();
    });
    it("gets number of pages", function () {
      expect(pdfDocument.numPages).toEqual(3);
    });