PDF seems ok to me but I cannot read because of chinese characters (Win XP/Acrobar reader). You might want to check your system.

Please provide a link to an activated test survey.

Please also check the server's error logs if there are any hints.

I ever test with russion, never have problem.

For chinese:
$config['alternatepdffontfile']=array(
'ar'=>'dejavusans',// 'dejavusans' work but maybe more characters in aealarabiya or almohanad: but then need a dynamic font size too
'be'=>'dejavusans',
'bg'=>'dejavusans',
'zh-Hans'=>'chinese',
'zh-Hant-HK'=>'chinese',
'zh-Hant-TW'=>'chinese',
'cs'=>'dejavusans',
'cs-informal'=>'dejavusans',// This one not really tested: no translation for Yes/No or Gender
'el'=>'dejavusans',
'he'=>'freesans',
'hi'=>'dejavusans',
'hu'=>'dejavusans',
'ja'=>'cid0jp',
'ko'=>'cid0kr',
'lv'=>'dejavusans',
'lt'=>'dejavusans',
'mk'=>'dejavusans',
'mt'=>'dejavusans',
'fa'=>'dejavusans',
'pl'=>'dejavusans',
'pa'=>'freesans',
'ro'=>'dejavusans',
'ru'=>'dejavusans',
'sr'=>'dejavusans',
);

Hi Mfaber,
you mean the attached pdf file displayed something in your computer?
when i open this pdf, you can find this is blank file, nothing displayed like the attached jpg file, it's my screenshot.

yes. Can't read it but it sure looks chinese :).
See screenshot.

checked your screenshot, it displayed chinese well.
BUT i use acrobat9 to read this file, displayed nothing.
i hope it's the pdf reader problem,not the pdf output function problem

This was a Win7 machine with sumatra pdf reader. My first try (from july, see above) was on a win xp machine with acrobat reader. I do not remember which version but probably the newest at that time. Strange...

Looks fine here too - not a LimeSurvey bug.