QPdfDocument::getAllText missing characters

QPdfDocument::getAllText does not return all characters, some characters are missing. Please check the out.pdf I posted. The out.txt is generated by fitz+PyMuPDF:

python3 -m fitz gettext -pages 1 out.pdf

It works fine. But result from QPdfDocument::getAllText missing some charactors, I put the result in getAllText.txt file. Here is the diff :

getAllText: 是一个共享 ，供 个 系 统 （如在计算 机之

PyMuPDF: 接口是一个共享框架，供 两 个 系 统 （如在计算机和打印机之间

As it shows , a lot character are missing. I think pdfium returned wrong result, but chrome can handle this pdf correctly (copy works fine, along with other pdf viewers ). May be it's relevant to chromium version Qt used?