PDF Document does not print all Fields generated with iText

With the help of iText we patch some fields in already existing PDF documents.
This was no problem so far.
But recently some Windows PC can print the whole document and others have
the document but not the patched fields.

After some investigation of the problem, the reason was, that the fields use
an unicode font.
The AdobeReader was extended with the FontPack.
This allows the usage of e.g arabic fonts.
But when a Reader has not the FontPack, the PDF document with the unicode
font can be viewed and everything is fine, but this part of the document is
not printed.

Just changing the font to something else works quite fine.