php everywhere read file

this plugin is very good. I could insert php code in php+html widget. thank you.
when php try to read a file
<?php
$myfile = fopen(“abc.txt”, “r”) or die(“Unable to open file!”);
echo fread($myfile,filesize(“abc.txt”));
fclose($myfile);
?>
I got error,
Warning: fopen(abc.txt): failed to open stream: No such file or directory in C:\xampp\htdocs\wp6\wp-content\plugins\php-everywhere\widget.php(45) : eval()’d code on line 9
Unable to open file!
I put abc.txt in C:\xampp\htdocs\wp6\wp-content\plugins\php-everywhere\
got same error.
so, where should I put abc.txt for php to read?

thanks
Xian