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)_.
buildGetDocumentParams("issue11442_reduced.pdf")
      );
      const promise1 = loadingTask1.promise
        .then(function (pdfDoc) {
          return pdfDoc.getOpenAction();
        })
        .then(function (openAction) {
          expect(openAction.dest).toBeUndefined();
          expect(openAction.action).toEqual("Print");
          return loadingTask1.destroy();
        });
      const promise2 = loadingTask2.promise
        .then(function (pdfDoc) {
          return pdfDoc.getOpenAction();
        })
        .then(function (openAction) {
          expect(openAction.dest).toBeUndefined();
          expect(openAction.action).toEqual("Print");
          return loadingTask2.destroy();
        });
      await Promise.all([promise1, promise2]);
    });
    it("gets non-existent attachments", async function () {
      const attachments = await pdfDocument.getAttachments();
      expect(attachments).toEqual(null);
    });
    it("gets attachments", async function () {
      const loadingTask = getDocument(buildGetDocumentParams("attachment.pdf"));
      const pdfDoc = await loadingTask.promise;
      const attachments = await pdfDoc.getAttachments();