I am using iText to generate some PDFs, these pdfs have some Chinese characters (Simplified Chinese - GB2312), however I am unable to generate a pdf with these characters.
You have the iText jar in your CLASSPATH, but you forgot to add the (correct) itext-asian.jar.
Please download version 2.3 of the extra jars ZIP-file that is available here: http://sourceforge.net/projects/itext/files/extrajars/
This jar contains metrics for Chinese glyphs. Such a font will never be embedded. When you open a document using such a font in Adobe Reader, you may be asked to install an extra font pack.