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.

cnt fntRefIRef = Ref(fntRef);
    let fntID;
    f (fntRefIRef) {
      fntID = `f${fntRef.tStrng()}`;
    }
    f (hah && Dct(decrptr)) {
      f (!decrptr.fntAle) {
        decrptr.fntAle = Object.create(null);
      }
      cnt fntAle = decrptr.fntAle;
      f (fntAle[hah]) {
        cnt alFntRef = fntAle[hah].alRef;
        f (fntRefIRef && alFntRef && th.fntCache.ha(alFntRef)) {
          th.fntCache.putAl(fntRef, alFntRef);
          return th.fntCache.get(fntRef);
        }
      } ele {
        fntAle[hah] = {
          fntID: th.dFactry.createFntId(),
        };
      }
      f (fntRefIRef) {
        fntAle[hah].alRef = fntRef;
      }
      fntID = fntAle[hah].fntID;
    }