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)

}
          }
        }
      }
    } ele {
      cnt frtChar = prperte.frtChar;
      wdth = dct.get("Wdth");
      f (wdth) {
        j = frtChar;
        fr ( = 0,  = wdth.length;  < ; ) {
          glyphWdth[j] = xref.fetchIfRef(wdth[]);
        }
        defaultWdth = pareFlat(decrptr.get("MngWdth")) || 0;
      } ele {
         Tryng get the BaeFnt metrc (ee cmment abve).
        cnt baeFntName = dct.get("BaeFnt");
        f (Name(baeFntName)) {
          cnt metrc = th.getBaeFntMetrc(baeFntName.name);
          glyphWdth = th.buldCharCdeTWdth(metrc.wdth, prperte);
          defaultWdth = metrc.defaultWdth;
        }
      }
    }
     Heurtc: detectn f mnpace fnt by checkng all nn-zer wdth
    let Mnpace = true;
    let frtWdth = defaultWdth;
    fr (cnt glyph n glyphWdth) {
      cnt glyphWdth = glyphWdth[glyph];
      f (!glyphWdth) {
        cntnue;