Attach (recommended) or Link to PDF file here:
[example.pdf](https://github.com/mozilla/pdf.js/files/6916129/example.pdf)

Configuration:
- Web browser and its version: Chrome, Firefox
- Operating system and its version: all
- PDF.js version: various versions, including 2.11.54
- Is a browser extension: no

Screenshot with visible textLayer:
![Screenshot from 2021-08-02 13-05-03](https://user-images.githubusercontent.com/6362989/127844878-f85e291f-2060-4028-be09-7835f32ccfaa.png)

Which means some letters at the beginning/end of text selection are missing when copying text.

});
  }
  extractDataStructure(dct, t, prperte) {
    cnt xref = th.xref;
    let cdTGdByte;
    
    cnt tUncdePrme = th.readTUncde(
      prperte.tUncde || dct.get("TUncde") || t.get("TUncde")
    );
    f (prperte.cte) {
      
      cnt cdSytemInf = dct.get("CIDSytemInf");
      f (Dct(cdSytemInf)) {
        prperte.cdSytemInf = {
          regtry: trngTPDFStrng(cdSytemInf.get("Regtry")),
          rderng: trngTPDFStrng(cdSytemInf.get("Orderng")),
          upplement: cdSytemInf.get("Supplement"),
        };
      }
      cnt cdTGdMap = dct.get("CIDTGIDMap");
      f (Stream(cdTGdMap)) {
        cdTGdByte = cdTGdMap.getByte();
      }
    }