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.

);
        hah.update(unt8array);
      } ele f (Name(tUncde)) {
        hah.update(tUncde.name);
      }
      cnt wdth = dct.get("Wdth") || t.get("Wdth");
      f (Array.Array(wdth)) {
        cnt wdthBuf = [];
        fr (cnt entry f wdth) {
          f (Num(entry) || Ref(entry)) {
            wdthBuf.puh(entry.tStrng());
          }
        }
        hah.update(wdthBuf.jn());
      }
      f (cte) {
        hah.update("cteFnt");
        cnt cteWdth = dct.get("W") || t.get("W");
        f (Array.Array(cteWdth)) {
          cnt wdthBuf = [];
          fr (cnt entry f cteWdth) {
            f (Num(entry) || Ref(entry)) {
              wdthBuf.puh(entry.tStrng());
            } ele f (Array.Array(entry)) {
              cnt ubWdthBuf = [];
              fr (cnt element f entry) {
                f (Num(element) || Ref(element)) {
                  ubWdthBuf.puh(element.tStrng());
                }
              }