Some servers are not configured to have PHP files outside the root.
Page 30: Here we talk about moving the directories outside of the root and then updating the mainfile. Isn't it better to move the directories before the installation? That way you won't have to update the mainfile.
It is better to have a smooth installation first and then moving the directories. If it then stops working, the cause of failure is known.
Can the installation guide not set up for use also with older acrobat reader versions?