This directive sets the directory from which httpd will serve files. Unless matched by a directive like Alias, the server appends the path from the requested URL to the document root to make the path to the document.
# Example:
DocumentRoot "/usr/web"
then an access to:
http://my.example.com/index.html
refers to:
/usr/web/index.html
If the directory-path is not absolute then it is assumed to be relative to the ServerRoot.
The DocumentRoot should be specified without a trailing slash apache.org 
To find the Apache Document Root use grep command as follows:
# grep -i 'DocumentRoot' httpd.conf
# Livecode Env Variable
In Livecode server the value of document root can be derived using:
put $_SERVER ["DOCUMENT_ROOT"] & slash into docRoot