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 basicApiFileName = "basicapi.pdf";
  const basicApiFileLength = 105779; 
  const basicApiGetDocumentParams = buildGetDocumentParams(basicApiFileName);
  let CanvasFactory;
  beforeAll(function () {
    CanvasFactory = new DefaultCanvasFactory();
  });
  afterAll(function () {
    CanvasFactory = null;
  });
  function waitSome(callback) {
    const WAIT_TIMEOUT = 10;
    setTimeout(function () {
      callback();
    }, WAIT_TIMEOUT);
  }
  describe("getDocument", function () {
    it("creates pdf doc from URL-string", async function () {
      const urlStr = TEST_PDFS_PATH + basicApiFileName;
      const loadingTask = getDocument(urlStr);
      expect(loadingTask instanceof PDFDocumentLoadingTask).toEqual(true);
      const pdfDocument = await loadingTask.promise;
      expect(typeof urlStr).toEqual("string");
      expect(pdfDocument instanceof PDFDocumentProxy).toEqual(true);
      expect(pdfDocument.numPages).toEqual(3);
      await loadingTask.destroy();
    });
    it("creates pdf doc from URL-object", async function () {
      if (isNodeJS) {
        pending("window.location is not supported in Node.js.");