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);
  if (
     header[0] >= 1 &&
    
    
     header[3] >= 1 &&
    header[3] <= 4
  ) {
    return true;
  }
  return false;
}
function getFontFileType(file, { type, subtype, composite }) {
  let fileType, fileSubtype;
  if (isTrueTypeFile(file) || isTrueTypeCollectionFile(file)) {
    if (composite) {
      fileType = "CIDFontType2";
    } else {
      fileType = "TrueType";
    }
  } else if (isOpenTypeFile(file)) {
    if (composite) {
      fileType = "CIDFontType2";