Default page size is set to A4. In the Custom Paper Size window, I can't
change the page size and save the settings. A popup window tells me to
delete some of the stored page sizes to save my customized version. I am
unable to delete any of the pre-stored document sizes and hence unable to
create a custom paper size. Incidentally, the range of pre-stored document
sizes omits the F4 paper size (8.26 x 13 inch).