What you're trying to do will be very complicated -- depending on what exactly you want to do with the CGI file. If all you want to do is read it character-for-character, and output the code (not the result of the code's execution), then it's not a problem:
$fp = file("script.cgi");
$eof = count($file);
for ($i=0;$i<$eof;$i++) {
echo $fp[$i] . "<br>";
}
That will just output the code as it is in the editor (which is probably not what you intended)
However, if you are trying execute the code, that will be somewhat complicated. using include() or require() will try to execute the script, but, obviously will not work due to incompatibility. You can search the manual for topics on working with CGI scripts.