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)

return pdfDoc.getOpenAction();
        })
        .then(function (openAction) {
          expect(openAction.dest).toBeUndefined();
          expect(openAction.action).toEqual("Print");
          return loadingTask2.destroy();
        });
      await Promise.all([promise1, promise2]);
    });
    it("gets non-existent attachments", async function () {
      const attachments = await pdfDocument.getAttachments();
      expect(attachments).toEqual(null);
    });
    it("gets attachments", async function () {
      const loadingTask = getDocument(buildGetDocumentParams("attachment.pdf"));
      const pdfDoc = await loadingTask.promise;
      const attachments = await pdfDoc.getAttachments();
      const attachment = attachments["foo.txt"];
      expect(attachment.filename).toEqual("foo.txt");
      expect(attachment.content).toEqual(
        new Uint8Array([98, 97, 114, 32, 98, 97, 122, 32, 10])
      );
      await loadingTask.destroy();
    });
    it("gets javascript", async function () {
      const javascript = await pdfDocument.getJavaScript();
      expect(javascript).toEqual(null);
    });
    it("gets javascript with printing instructions (JS action)", async function () {