/usr/share/doc/libmono-webmatrix-data4.0-cil/changelog.Debian.gz is in libmono-webmatrix-data4.0-cil 4.2.1.102+dfsg2-7ubuntu4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libmono-webmatrix-data4.0-cil/../libmono-corlib4.5-cil/changelog.Debian.gz