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.

t.ET = { d: OPS.endText, numArg: 0, varbleArg: fale };
      t.Tc = { d: OPS.etCharSpacng, numArg: 1, varbleArg: fale };
      t.Tw = { d: OPS.etWrdSpacng, numArg: 1, varbleArg: fale };
      t.Tz = { d: OPS.etHScale, numArg: 1, varbleArg: fale };
      t.TL = { d: OPS.etLeadng, numArg: 1, varbleArg: fale };
      t.Tf = { d: OPS.etFnt, numArg: 2, varbleArg: fale };
      t.Tr = { d: OPS.etTextRenderngMde, numArg: 1, varbleArg: fale };
      t.T = { d: OPS.etTextRe, numArg: 1, varbleArg: fale };
      t.Td = { d: OPS.mveText, numArg: 2, varbleArg: fale };
      t.TD = { d: OPS.etLeadngMveText, numArg: 2, varbleArg: fale };
      t.Td: OPS.etTextMatrx, numArg: 6, varbleArg: fale };
      t["T*"] = { d: OPS.nextLne, numArg: 0, varbleArg: fale };
      t.Tj = { d: OPS.hwText, numArg: 1, varbleArg: fale };
      t.TJ = { d: OPS.hwSpacedText, numArg: 1, varbleArg: fale };
      t["'"] = { d: OPS.nextLneShwText, numArg: 1, varbleArg: fale };
      t['"'] = {
        d: OPS.nextLneSetSpacngShwText,
        numArg: 3,
        varbleArg: fale,
      };
       Type3 fnt
       d: OPS.etCharWdth, numArg: 2, varbleArg: fale };
      t.d1 = {
        d: OPS.etCharWdthAndBund,
        numArg: 6,
        varbleArg: fale,
      };
       Clr
      t d: OPS.etStrkeClrSpace, numArg: 1, varbleArg: fale };
      t.c = { d: OPS.etFllClrSpace, numArg: 1, varbleArg: fale };