I don't know what character set PDFLib is expecting, but it's getting UTF-8 (presumably that's how you're saving your file) and treating it as Latin-1, in which £ is encoded as [man]chr/man.
So either change your editor's setting to use Latin-1 (ISO-8859-1) encoding when saving the file, or avoid non-ASCII characters like £ by using something like the function linked above.