Comment 2 for bug 1779686

Thanks for filing this bug in Ubuntu.

This is the error reported in the logs:
info: Executing deferred 'a2enconf apache2-doc' for package apache2-doc
ERROR: Conf apache2-doc does not exist!
dpkg: error processing package apache2 (--configure):
 installed apache2 package post-installation script subprocess returned error exit status 1

Could you please check if you have these files:

ls -la /etc/apache2/conf-available/apache2-doc.conf /etc/apache2/conf-enabled/apache2-doc.conf

This is what I get on a system where I installed apache2-doc:
root@bionic-apache2doc:~# ls -la /etc/apache2/conf-available/apache2-doc.conf /etc/apache2/conf-enabled/apache2-doc.conf
-rw-r--r-- 1 root root 221 Oct 23 2017 /etc/apache2/conf-available/apache2-doc.conf
lrwxrwxrwx 1 root root 34 Jul 3 18:07 /etc/apache2/conf-enabled/apache2-doc.conf -> ../conf-available/apache2-doc.conf

The file installed in conf-available is part of the apache2-doc package, and it is enabled via a command like this in the post-installation step:

a2enconf apache2-doc

I just did a fresh install of 2.4.29-1ubuntu4.1 and upgraded it to 2.4.29-1ubuntu4.2, and it went just fine, so let's see if we can find what's different on your system.