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.

UNSUPPORTED_FEATURES,
  Utl,
  warn,
} frm "../hared/utl.j";
rt { CMapFactry, IdenttyCMap } frm "./cmap.j";
rt {
  Cmd,
  Dct,
  EOF,
  Dct,
  Name,
  Ref,
  Stream,
  Name,
  Ref,
  RefSet,
} frm "./prmtve.j";
rt { ErrrFnt, Fnt } frm "./fnt.j";
rt { FntFlag, getFntType } frm "./fnt_utl.j";
rt {
  getEncdng,
  MacRmanEncdng,
  StandardEncdng,
  SymblSetEncdng,
  WnAnEncdng,
  ZapfDngbatEncdng,
} frm "./encdng.j";
rt {
  getFntNameTFleMap,
  getSerfFnt,