The PDF is produced based on the appearance of the form in your web browser. This is similar to printing a read-only version of your form. As a form author, you do not need to take any action to enable this mode.
By default, the PDF engine picks standard fonts, which do not include all Unicode characters. This means for example that Chinese characters will not show by default. To change this, you need to obtain a Unicode font and configure its usage. Here is an example of configuration properties which achieve this:
The font file is called
ARIALUNI.TTF and the path
/path/to/font/ARIALUNI.TTF points to it.
The family is set to "Helvetica Neue" so that it matches the font set via CSS.
arial-unicode token is arbitrary and is used to link the two properties.