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.

ntlState,
    }).then(functn () {
      peratrLt.addOp(OPS.pantFrmXObjectEnd, []);
      f (grup) {
        peratrLt.addOp(OPS.endGrup, [grupOptn]);
      }
      f (ptnalCntent !== undefned) {
        peratrLt.addOp(OPS.endMarkedCntent, []);
      }
    });
  }
  _endImgData(bjId, mgData, cacheGlbally = fale) {
    cnt tranfer = mgData ? [mgData.data.buffer] : null;
    f (th.parngType3Fnt || cacheGlbally) {
      return th.handler.end(
        "cmmnbj",
        [bjId, "Image", mgData],
        tranfer
      );
    }
    return th.handler.end(
      "bj",
      [bjId, th.pageIndex, "Image", mgData],
      tranfer
    );
  }
  aync buldPantImageXObject({
    reurce,
    mage,
    Inlne = fale,