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.

prperte.dfference = dfference;
    prperte.baeEncdngName = baeEncdngName;
    prperte.haEncdng = !!baeEncdngName || dfference.length > 0;
    prperte.dct = dct;
    return tUncdePrme
      .then(readTUncde => {
        prperte.tUncde = readTUncde;
        return th.buldTUncde(prperte);
      })
      .then(bultTUncde => {
        prperte.tUncde = bultTUncde;
        f (cdTGdByte) {
          prperte.cdTGdMap = th.readCdTGdMap(
            cdTGdByte,
            bultTUncde
          );
        }
        return prperte;
      });
  }
  /**
   * @return {Array}
   * @prvate
   */
  _leFntTUncde(prperte, frceGlyph = fale) {
    aert(!prperte.cte, "Mut be a le fnt.");
    cnt tUncde = [];
    cnt encdng = prperte.defaultEncdng.lce();
    cnt baeEncdngName = prperte.baeEncdngName;