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)

let firstImgData = null;
      for (let i = 1; i <= pdfDoc.numPages; i++) {
        const pdfPage = await pdfDoc.getPage(i);
        const opList = await pdfPage.getOperatorList();
        const { commonObjs, objs } = pdfPage;
        const imgIndex = opList.fnArray.indexOf(OPS.paintImageXObject);
        const [objId, width, height] = opList.argsArray[imgIndex];
        if (i < NUM_PAGES_THRESHOLD) {
          expect(objId).toEqual(`img_p${i - 1}_1`);
          expect(objs.has(objId)).toEqual(true);
          expect(commonObjs.has(objId)).toEqual(false);
        } else {
          expect(objId).toEqual(
            `g_${loadingTask.docId}_img_p${NUM_PAGES_THRESHOLD - 1}_1`
          );
          expect(objs.has(objId)).toEqual(false);
          expect(commonObjs.has(objId)).toEqual(true);
        }
        expect(width).toEqual(EXPECTED_WIDTH);
        expect(height).toEqual(EXPECTED_HEIGHT);
        
        if (i === 1) {
          firstImgData = objs.get(objId);
          expect(firstImgData.width).toEqual(EXPECTED_WIDTH);
          expect(firstImgData.height).toEqual(EXPECTED_HEIGHT);
          expect(firstImgData.kind).toEqual(ImageKind.RGB_24BPP);
          expect(firstImgData.data instanceof Uint8ClampedArray).toEqual(true);
          expect(firstImgData.data.length).toEqual(25245000);
        } else {
          const objsPool = i >= NUM_PAGES_THRESHOLD ? commonObjs : objs;