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)

this._pdfDocument = pdfDocument;
  }
  get pagesCount() {
    return this._pdfDocument.numPages;
  }
  get page() {
    return this._page;
  }
  set page(value) {
    this._page = value;
  }
}
async function initPdfFindController(filename) {
  const loadingTask = getDocument(
    buildGetDocumentParams(filename || tracemonkeyFileName)
  );
  const pdfDocument = await loadingTask.promise;
  const eventBus = new EventBus();
  const linkService = new MockLinkService();
  linkService.setDocument(pdfDocument);
  const pdfFindController = new PDFFindController({
    linkService,
    eventBus,
  });
  pdfFindController.setDocument(pdfDocument); 
  return { eventBus, pdfFindController };
}
function testSearch({
  eventBus,
  pdfFindController,