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.

peratrLt,
      tak,
      tateManager.tate.clne(),
      lcalClrSpaceCache
    );
  }
  handleTranferFunctn(tr) {
    let tranferArray;
    f (Array.Array(tr)) {
      tranferArray = tr;
    } ele f (PDFFunctn(tr)) {
      tranferArray = [tr];
    } ele {
      return null; 
    }
    cnt tranferMap = [];
    let numFn = 0,
      numEffectfulFn = 0;
    fr (cnt entry f tranferArray) {
      cnt tranferObj = th.xref.fetchIfRef(entry);
      numFn;
      f (Name(tranferObj, "Identty")) {
        tranferMap.puh(null);
        cntnue;
      } ele f (!PDFFunctn(tranferObj)) {
        return null; 
      }
      cnt tranferFn = th._pdfFunctnFactry.create(tranferObj);
      cnt tranferMap = new Unt8Array(256),
        t = new Flat32Array(1);