Identical to readfile(), except that file() returns the file in an array. Each element of the array corresponds to a line in the file, with the newline still attached. Upon failure, file() returns FALSE.
and then, that file doesn't need to be touched, get the md5 hashsum of the file and validate it in the other script you mentioned. copyright.php should not need updating after it contains the standard copyright info meaning the md5 hash will not change?
Before you got and invest a least a few hundred bucks in the Zend Encoder or SafeGuard Suite (the Zend Studio doesn't have encoding abilities - it can only link with the Encoder/SafeGuard Suite to do that) you might want to take a look at ioncube.com. They have an encoder that is just as good (and in many cases better) than what Zend provides. To top it off, it only costs $199.
What you need to do is two fold:
a) Prevent someone editing the Copyright notice
b) Prevent someone from removing the Copyright include inside your files
If you use the md5 file stuff you should be able to prevent anyone editing the Copyright notice. After that, it's a simple case of setting up your script and encoding a number of files where the Copyright notice is included and validated.