Thank you for reporting this problem. Our team was able to find out that the problem is how PHP binding interprets C's char data type as UTF-8 char. Our C/C++ interface returns char data type for the Date class's month, day, hour, and so on.
This issue will be addressed as part of the next PDFNetC update. In the meantime, you can work around this issue by using the ord
functions of PHP to get the correct values.