PDF files:
[1.pdf](https://github.com/mozilla/pdf.js/files/2955999/1.pdf)
[2.pdf](https://github.com/mozilla/pdf.js/files/2956000/2.pdf)
[3.pdf](https://github.com/mozilla/pdf.js/files/2956002/3.pdf)

Configuration:
- Web browser and its version: Chrome, Firefox
- Operating system and its version: Ubuntu, macOS
- PDF.js version: 2.2.42, but the same was with 2.1.x, and with https://mozilla.github.io/pdf.js/web/viewer.html
- Is a browser extension: no

Steps to reproduce the problem:
1. Select text
2. Copy text

What went wrong?

Getting this:
`OpenSansisahumanistsansseriftypefacedesignedbySteveMatteson.OpenSanswasdesignedwithanuprightstress,openformsandaneu-tral,yetfriendlyappearance.Itwasoptimizedforprint,web,andmobileinterfaces,andhasexcellentlegibilitycharacteristicsinitsletterforms(seefigureonthefollowingpage).ThisfontisavailablefromtheGoogleFontDirectory[]asTrueTypefileslicensedundertheApacheLicenseversion..`

Instead of this:
`Open Sans is a humanist sans serif typeface designed by Steve Matteson.
Open Sans was designed with an upright stress, open forms and a neutral,
yet friendly appearance. It was optimized for print, web, and mobile
interfaces, and has excellent legibility characteristics in its letterforms (see
figure 1 on the following page). This font is available from the Google Font
Directory [1] as TrueType files licensed under the Apache License version 2.0.`

This is quite significant problem, because I would say 1/20 of scientific papers encounter this problem.

}
         e) Map the CID btaned n tep (a) accrdng t the CMap
         btaned n tep (d), prducng a Uncde value.
        cnt uc2 = uc2CMap.lkup(cd);
        f (uc2) {
          tUncde[charcde] = Strng.frmCharCde(
            (uc2.charCdeAt(0) << 8)  uc2.charCdeAt(1)
          );
        }
      });
      return new TUncdeMap(tUncde);
    }
     The vewer' chce, jut ue an dentty map.
    return new IdenttyTUncdeMap(prperte.frtChar, prperte.latChar);
  }
  readTUncde(cmapObj) {
    f (!cmapObj) {
      return Prme.relve(null);
    }
    f (Name(cmapObj)) {
      return CMapFactry.create({
        encdng: cmapObj,
        fetchBultInCMap: th._fetchBultInCMapBund,
        ueCMap: null,
      }).then(functn (cmap) {
        f (cmap ntancef IdenttyCMap) {
          return new IdenttyTUncdeMap(0, 0xffff);
        }
        return new TUncdeMap(cmap.getMap());
      });