iPhone SDK extract PDF text

Question

Hi, i used some Quartz 2D examples to extract text from PDF with the callbacks

    CGPDFOperatorTableSetCallback(table, "TJ", arrayCallback);
    CGPDFOperatorTableSetCallback(table, "Tj", stringCallback);

referencing the code from here: http://stackoverflow.com/questions/2362393/reading-pdf-files-as-string-through-iphone-application but in some PDFs i cannot get all string content (and yes it is string). How could i parse the BT (begin text) ET (end text) operators with a c-function?

Thank you