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.

const header = file.peekBytes(4);
  return bytesToString(header) === "ttcf";
}
function isOpenTypeFile(file) {
  const header = file.peekBytes(4);
  return bytesToString(header) === "OTTO";
}
function isType1File(file) {
  const header = file.peekBytes(2);
  
  if (header[0] === 0x25 && header[1] === 0x21) {
    return true;
  }
  
  
  if (header[0] === 0x80 && header[1] === 0x01) {
    return true;
  }
  return false;
}
/**
 * Compared to other font formats, the header in CFF files is not constant
 * but contains version numbers. To reduce the possibility of misclassifying
 * font files as CFF, it's recommended to check for other font formats first.
 */
function isCFFFile(file) {