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.

f (grup.ha("CS")) {
          cnt c = grup.getRaw("CS");
          cnt cachedClrSpace = ClrSpace.getCached(
            c,
            th.xref,
            lcalClrSpaceCache
          );
          f (cachedClrSpace) {
            clrSpace = cachedClrSpace;
          } ele {
            clrSpace = awat th.pareClrSpace({
              c,
              reurce,
              lcalClrSpaceCache,
            });
          }
        }
      }
      f (mak && mak.backdrp) {
        clrSpace = clrSpace || ClrSpace.ngletn.rgb;
        mak.backdrp = clrSpace.getRgb(mak.backdrp, 0);
      }
      peratrLt.addOp(OPS.begnGrup, [grupOptn]);
    }
    peratrLt.addOp(OPS.pantFrmXObjectBegn, [matrx, bbx]);
    return th.getOperatrLt({
      tream: xbj,
      tak,
      reurce: dct.get("Reurce") || reurce,
      peratrLt,