That's a bit more modern than the old way where pointers to two
integers had to be passed to the method.

With the new method you can write

  auto pdfVersion = doc->getPdfVersion();
  // access numbers as pdfVersion.major and pdfVersion.minor

instead of

  int major, minor;
  doc->getPdfVersion(&major, &minor);

With C++17 you can even write

  auto [major, minor] = doc->getPdfVersion();

The new method is put alongside the old one in the Qt5 interface.
It replaces the old one in the Qt6 interface.