This file is indexed.

/etc/xdg/kaddressbook.categories is in kaddressbook 4:17.12.3-0ubuntu1.

This file is owned by root:root, with mode 0o644.

The actual contents of the file can be viewed below.

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org.kde.pim.kaddressbook kaddressbook (kaddressbook)
org.kde.pim.kaddressbook_plugin kaddressbook (kaddressbook kontact plugins)