Fatal Error

hi
with gravity form 1.7.6 and gravity form pdf 3.1.4, when i try to send a form i receive this error message

Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 131073 bytes) in /web/htdocs/www………..com/home/wp-content/plugins/gravity-forms-pdf-extended/mPDF/classes/ttfontsuni.php on line 1747

can you help me please?

http://ww.wp.xz.cn/plugins/gravity-forms-pdf-extended/