Encoding php file

str_rot13()
base64_decode()

Try ionCube PHP Encoder, 

link - http://www.ioncube.com/sa_encoder.php 

There are only two worthwhile players in the encoding market, Zend Guard ($600) and ionCube Encoder ($200). Both provide a similar level of protection and both require a binary module be installed on the server. In my unfortunate experience with this, it's frequently easier to convince web hosting providers to install Zend Guard due to Zend's relationship with the PHP development team. You're going to get a better user experience with Zend Guard, but ionCube is cheaper.
I'm still not going to recommend either of them. Your selection will ultimately depend on whether you can mandate that the user install the required binary extension. If you're targeting users on shared hosting, Zend Guard will win this requirements hands down. Some software providers that desire encryption frequently offer both, so the customer can decide which one works better for them.