Attach (recommended) or Link to PDF file here:

Configuration:
- Web browser and its version: Version 81.0.4044.138 (Official Build) (32-bit)
- Operating system and its version: Windows 10
- PDF.js version: latest
- Is a browser extension: no

Steps to reproduce the problem:

1. Open https://mozilla.github.io/pdf.js/web/viewer.html
2. Open the provided document
3. ctrl + F  and search for 'costs' .
4. Search for 'costs' - match NOT found.
5. Click the 'Download' and open the file in Adobe Reader, and search for costs - match is found.

What is the expected behavior? (add screenshot)
The word 'costs' to be returned by search

What went wrong? (add screenshot)
No results found

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):  https://mozilla.github.io/pdf.js/web/viewer.html
[2001_IESC_63_5_v6.pdf](https://github.com/mozilla/pdf.js/files/4644486/2001_IESC_63_5_v6.pdf)

const page1 = loadingTask.promise.then(function (pdfDoc) {
        return pdfDoc.getPage(1).then(
          function (pdfPage) {
            expect(pdfPage instanceof PDFPageProxy).toEqual(true);
            expect(pdfPage.ref).toEqual({ num: 6, gen: 0 });
          },
          function (reason) {
            throw new Error("shall not fail for valid page");
          }
        );
      });
      const page2 = loadingTask.promise.then(function (pdfDoc) {
        return pdfDoc.getPage(2).then(
          function (pdfPage) {
            throw new Error("shall fail for invalid page");
          },
          function (reason) {
            expect(reason instanceof Error).toEqual(true);
            expect(reason.message).toEqual(
              "Pages tree contains circular reference."
            );
          }
        );
      });
      await Promise.all([page1, page2]);
      await loadingTask.destroy();
    });
    it("gets page index", async function () {
      const ref = { num: 17, gen: 0 }; 
      const pageIndex = await pdfDocument.getPageIndex(ref);