There must be a way of making it permanent without editing one or more files.
No, theres not. As MasterC said, you need to add the line:
to the ~/.bash_profile file.
Alternatively, since there is only one executable in the Acrobat5 bin directory, simply make a symbolic link to acroread somewhere in your PATH:
ln -s /usr/local/Acrobat5/bin/acroread /usr/bin
Then you can start acrobat by typing "acroread" in the xterm.
I hope this helps