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)

it("gets fingerprints", function () {
      expect(pdfDocument.fingerprints).toEqual([
        "ea8b35919d6279a369e835bde778611b",
        null,
      ]);
    });
    it("gets fingerprints, from modified document", async function () {
      const loadingTask = getDocument(
        buildGetDocumentParams("annotation-tx.pdf")
      );
      const pdfDoc = await loadingTask.promise;
      expect(pdfDoc.fingerprints).toEqual([
        "3ebd77c320274649a68f10dbf3b9f882",
        "e7087346aa4b4ae0911c1f1643b57345",
      ]);
      await loadingTask.destroy();
    });
    it("gets page", async function () {
      const data = await pdfDocument.getPage(1);
      expect(data instanceof PDFPageProxy).toEqual(true);
      expect(data.pageNumber).toEqual(1);
    });
    it("gets non-existent page", async function () {
      let outOfRangePromise = pdfDocument.getPage(100);
      let nonIntegerPromise = pdfDocument.getPage(2.5);
      let nonNumberPromise = pdfDocument.getPage("1");
      outOfRangePromise = outOfRangePromise.then(
        function () {
          throw new Error("shall fail for out-of-range pageNumber parameter");
        },