what does your /var/log/cups/cups-pdf_log say?
if it says "[ERROR] failed to create directory (/home/username/PDF)" then your home directory possibly lacks the permissions required by cups-pdf
try:
ls -l /home
to check the permissions on your users' directories
what does your /var/log/ cups/cups- pdf_log say?
if it says "[ERROR] failed to create directory (/home/ username/ PDF)" then your home directory possibly lacks the permissions required by cups-pdf
try:
ls -l /home
to check the permissions on your users' directories