/etc/xdg/kpimtextedit.categories is in libkf5pimtextedit-dev 17.12.3-0ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1
org.kde.pim.kpimtextedit kpimtextedit (kpimtextedit)