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)

buildGetDocumentParams("issue9972-3.pdf")
      );
      const promise2 = loadingTask2.promise.then(function (pdfDoc) {
        return pdfDoc.getPermissions();
      });
      const totalPermissionCount = Object.keys(PermissionFlag).length;
      const permissions = await Promise.all([promise0, promise1, promise2]);
      expect(permissions[0].length).toEqual(totalPermissionCount - 1);
      expect(
        permissions[0].includes(PermissionFlag.MODIFY_CONTENTS)
      ).toBeFalsy();
      expect(permissions[1].length).toEqual(totalPermissionCount - 2);
      expect(permissions[1].includes(PermissionFlag.PRINT)).toBeFalsy();
      expect(
        permissions[1].includes(PermissionFlag.PRINT_HIGH_QUALITY)
      ).toBeFalsy();
      expect(permissions[2].length).toEqual(totalPermissionCount - 1);
      expect(permissions[2].includes(PermissionFlag.COPY)).toBeFalsy();
      await Promise.all([
        loadingTask0.destroy(),
        loadingTask1.destroy(),
        loadingTask2.destroy(),
      ]);
    });
    it("gets metadata", async function () {
      const { info, metadata, contentDispositionFilename, contentLength } =
        await pdfDocument.getMetadata();
      expect(info.Title).toEqual("Basic API Test");
      
      expect(info.Custom).toEqual(undefined);