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)_.
return loadingTask.destroy();
      });
      await Promise.all(destroyPromises);
    });
    it("should correctly render PDFs in parallel", async function () {
      let baseline1, baseline2, baseline3;
      const promiseDone = renderPDF(pdf1)
        .then(function (data1) {
          baseline1 = data1;
          return renderPDF(pdf2);
        })
        .then(function (data2) {
          baseline2 = data2;
          return renderPDF(pdf3);
        })
        .then(function (data3) {
          baseline3 = data3;
          return Promise.all([
            renderPDF(pdf1),
            renderPDF(pdf2),
            renderPDF(pdf3),
          ]);
        })
        .then(function (dataUrls) {
          expect(dataUrls[0]).toEqual(baseline1);
          expect(dataUrls[1]).toEqual(baseline2);
          expect(dataUrls[2]).toEqual(baseline3);
          return true;
        });
      await promiseDone;