pageSize() / pageSizeF() do not take /UserUnit into account
The page size values returned by poppler-qt5 are incorrect for pages that define a custom /UserUnit.
/UserUnit is a float or decimal that scales the default conversion fraction of 1/72in - for a /UserUnit of 10, 1pt would mean 10/72in, for instance. Poppler currently does not take /UserUnit into account when calculating page size.
As the documentation indicates that the returned values of pageSize() / pageSizeF() always mean 1pt -> 1/72in, it would be expected that poppler internally multiplies the value retrieved from CropBox with the /UserUnit scale factor, if given.
Please see https://bugs.kde.org/show_bug.cgi?id=442280 for test files and more information.