Hi @shelteradmin,
if the above works, then it is most probably your /tmp folder access, where Frappe will temporarily store the pdf output. Try the above with the output file as /tmp/file.pdf and you should find the same error. Your /tmp should be drwxrwxrwt owned by root:root
By the way, the same topic is in Server error on trying to generate pdf, let use know once it is fixed 