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 currentImgData = objsPool.get(objId);
          expect(currentImgData.width).toEqual(firstImgData.width);
          expect(currentImgData.height).toEqual(firstImgData.height);
          expect(currentImgData.kind).toEqual(firstImgData.kind);
          expect(currentImgData.data instanceof Uint8ClampedArray).toEqual(
            true
          );
          expect(
            currentImgData.data.every((value, index) => {
              return value === firstImgData.data[index];
            })
          ).toEqual(true);
        }
      }
      await loadingTask.destroy();
      firstImgData = null;
    });
  });
  describe("Multiple `getDocument` instances", function () {
    
    
    const pdf1 = buildGetDocumentParams("tracemonkey.pdf");
    
    const pdf2 = buildGetDocumentParams("TAMReview.pdf");
    
    const pdf3 = buildGetDocumentParams("issue6068.pdf");
    const loadingTasks = [];
    
    
    async function renderPDF(filename) {