HTMLDOC Problem:

Htmldoc produced no pdf-output.
Commandline:

/usr/local/bin/htmldoc -t pdf13  --webpage -f /html/typo3temp/hd_wdU8PR - 2>/html/typo3temp/se_yoow0H

This is the (stderr) output of the htmldoc command without the htmldoc_append parameters:
If you see no errors here please check your htmldoc_append parameters too.

HTMLDOC(788655) INFO: HTMLDOC 1.9.15 starting in CGI mode.
HTMLDOC(788655) INFO: TMPDIR is "(null)"
HTMLDOC(788655) ERR005: PATH_INFO is not set in the environment!
Can't open display: