I need to place HTML pages in the server file system and create links to them from the Wiki pages so that I can view them. However the error 403 "Forbidden you don't have permission to access /data/media/.../1.html on this server"
When Apache is properly configured for DokuWiki, directory
/data is restricted. This is normal and should not be changed.
If you need to add your own HTML pages in the filesystem, place them in apache DocumenRoot (probably directory
/var/www/html[/m] since you use ubuntu) but in a folder that is not DokuWiki [m]data[/m] folder. You'll have to manually insert links. For example, if you have file [m]/var/www/html/1.html[/m], you need to write [m][[http://your.server/1.html]] in your wiki page in order to link to this page.