...the file can be only accessed by a specific IP...
At HFS console, press alt+f6 to edit events file, and add this:
[download]
{.if|{.match|myparticularfile.doc|%url%.}|{:{.if|{.!=|%ip%|127.0.0.1.}|{:{.disconnect.}:}.}:}.}
replace myparticularfile.doc with target file name (to block for most)
replace 127.0.0.1 with target IP address (to allow for one)
P.S. Other options instead of myparticularfile.doc may be /folder* or *.doc and you can even add to the list, such as myparticularfile.doc;myotherfile.txt;*.pdf with semicolon in-between.
P.P.S. If this method seems clunky, then you could use the more normal and flexible users/groups/passwords, located in hfs menu > other options > user accounts. And, then you can right-click on a particular folder/file to set it private to your users/groups.