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 pdfDoc = await loadingTask.promise;
      const pdfPage = await pdfDoc.getPage(1);
      const operatorList = await pdfPage.getOperatorList();
      expect(operatorList.fnArray.length).toBeGreaterThan(20);
      expect(operatorList.argsArray.length).toBeGreaterThan(20);
      expect(operatorList.lastChunk).toEqual(true);
      
      
      expect(operatorList.fnArray.includes(OPS.beginAnnotation)).toEqual(true);
      expect(operatorList.fnArray.includes(OPS.endAnnotation)).toEqual(true);
      await loadingTask.destroy();
    });
    it("gets operator list, with `annotationMode`-option", async function () {
      const loadingTask = getDocument(buildGetDocumentParams("evaljs.pdf"));
      const pdfDoc = await loadingTask.promise;
      const pdfPage = await pdfDoc.getPage(2);
      pdfDoc.annotationStorage.setValue("30R", { value: "test" });
      pdfDoc.annotationStorage.setValue("31R", { value: true });
      const opListAnnotDisable = await pdfPage.getOperatorList({
        annotationMode: AnnotationMode.DISABLE,
      });
      expect(opListAnnotDisable.fnArray.length).toEqual(0);
      expect(opListAnnotDisable.argsArray.length).toEqual(0);
      expect(opListAnnotDisable.lastChunk).toEqual(true);
      const opListAnnotEnable = await pdfPage.getOperatorList({
        annotationMode: AnnotationMode.ENABLE,
      });
      expect(opListAnnotEnable.fnArray.length).toBeGreaterThan(150);
      expect(opListAnnotEnable.argsArray.length).toBeGreaterThan(150);