HTMLDOC Problem:

Htmldoc produced no pdf-output.
Commandline:

/usr/bin/htmldoc -t pdf13  --webpage -f /home/www/doc/19521/dcp195210033/ttproducts.de/www/typo3temp/hd_UVhL7V - 2>/home/www/doc/19521/dcp195210033/ttproducts.de/www/typo3temp/se_hnqODQ

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(1481) INFO: HTMLDOC 1.8.27 starting in CGI mode.
HTMLDOC(1481) INFO: TMPDIR is "(null)"
HTMLDOC(1481) ERR005: PATH_INFO is not set in the environment!
Can't open display: