/usr/share/acl2-6.3/books/xdoc/ is in acl2-books-certs 6.3-5.
This file is owned by root:root, with mode 0o755.
..
/usr/share/acl2-6.3/books/xdoc/all.cert
/usr/share/acl2-6.3/books/xdoc/autolink.cert
/usr/share/acl2-6.3/books/xdoc/base.cert
/usr/share/acl2-6.3/books/xdoc/book-thms-example.cert
/usr/share/acl2-6.3/books/xdoc/book-thms.cert
/usr/share/acl2-6.3/books/xdoc/debug.cert
/usr/share/acl2-6.3/books/xdoc/defsection-tests.cert
/usr/share/acl2-6.3/books/xdoc/defxdoc-raw.cert
/usr/share/acl2-6.3/books/xdoc/display.cert
/usr/share/acl2-6.3/books/xdoc/fmt-to-str.cert
/usr/share/acl2-6.3/books/xdoc/import-acl2doc.cert
/usr/share/acl2-6.3/books/xdoc/importance.cert
/usr/share/acl2-6.3/books/xdoc/names.cert
/usr/share/acl2-6.3/books/xdoc/parse-xml.cert
/usr/share/acl2-6.3/books/xdoc/portcullis.cert
/usr/share/acl2-6.3/books/xdoc/prepare-topic.cert
/usr/share/acl2-6.3/books/xdoc/preprocess.cert
/usr/share/acl2-6.3/books/xdoc/save-classic.cert
/usr/share/acl2-6.3/books/xdoc/save-fancy.cert
/usr/share/acl2-6.3/books/xdoc/sort.cert
/usr/share/acl2-6.3/books/xdoc/spellcheck.cert
/usr/share/acl2-6.3/books/xdoc/top.cert
/usr/share/acl2-6.3/books/xdoc/topics.cert
/usr/share/acl2-6.3/books/xdoc/word-wrap.cert
/usr/share/acl2-6.3/books/xdoc/write-acl2-xdoc.cert