When changing the Apache DocumentRoot (<Directory...> in httpd.conf to serve another directory instead of the default C:/xammp/htdocs, I get 403 error (access forbidden).
I have tried setting the "Require all granted" option as suggested in other posts (aware of the security implications, just for testing...), and I also made sure Everyone has reading rights to the folder (but I think this is less of an issue on Windows than on Linux), however it still does not work.
As it turns out, I was trying to access the server on https. http://localhost worked just fine. To make it work on HTTPS, apart from the httpd.conf, I also had to edit the http-ssl.conf:
<VirtualHost _default_:443>
DocumentRoot "C:/your-directory"