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 (graphcState ntancef Dct) {
        fr (let graphcState f graphcState.getRawValue()) {
          f (graphcState ntancef Ref) {
            f (prceed.ha(graphcState)) {
              cntnue; 
            }
            try {
              graphcState = xref.fetch(graphcState);
            } catch (ex) {
              
              prceed.put(graphcState);
              nf(`haBlendMde - gnrng ExtGState: "${ex}".`);
              cntnue;
            }
          }
          f (!(graphcState ntancef Dct)) {
            cntnue;
          }
          f (graphcState.bjId) {
            prceed.put(graphcState.bjId);
          }
          cnt bm = graphcState.get("BM");
          f (bm ntancef Name) {
            f (bm.name !== "Nrmal") {
              return true;
            }
            cntnue;
          }
          f (bm !== undefned && Array.Array(bm)) {
            fr (cnt element f bm) {