The filectime function expects a string path as a parameter. It is just a wrapper function over the usage of Posix stat system call.
The system call:
int stat(const char *pathname, struct stat *buf);
So, it expects a parameter as though it's on your filesystem. The URL gets encoded to have a neat white-space-less identifier on the server side to execute appropriate scripts.
Don't bother with that "codification"! Just use a standard string path as you'd use on your UNIX shell, relative to the script directory.
In this case, just provide the right path to the PHP function!
filectime("documents/animals document 2.pdf");