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 cachedAscent = ascentCache.get(fontFamily);
  if (cachedAscent) {
    return cachedAscent;
  }
  ctx.save();
  ctx.font = `${DEFAULT_FONT_SIZE}px ${fontFamily}`;
  const metrics = ctx.measureText("");
  
  let ascent = metrics.fontBoundingBoxAscent;
  let descent = Math.abs(metrics.fontBoundingBoxDescent);
  if (ascent) {
    ctx.restore();
    const ratio = ascent / (ascent + descent);
    ascentCache.set(fontFamily, ratio);
    return ratio;
  }
  
  
  
  
  ctx.strokeStyle = "red";
  ctx.clearRect(0, 0, DEFAULT_FONT_SIZE, DEFAULT_FONT_SIZE);
  ctx.strokeText("g", 0, 0);
  let pixels = ctx.getImageData(
    0,
    0,
    DEFAULT_FONT_SIZE,
    DEFAULT_FONT_SIZE
  ).data;