Q: Sometimes, when I type in non-Latin characters in interactive PDF form fields, some characters vanish or disappear. Why is that so? What can I do to fix this?

A: The problem with non-Latin characters (Greek, Russian, Arabic, Hebrew) disappearing after being entered in an interactive text field has to do with the way that fonts and characters are stored in a PDF document. The PDF format was designed before Unicode, so characters are encoded in a single byte. Because of this, font descriptors can only contain 255 characters and to handle more than 255 characters, a string has to be broken up into sections with each section using a different font and character encoding definition. PDF Studio does not support this mechanism yet but we will add this very soon.

For now, supported characters in interactive form fields are the 255 characters that are defined in the font associated with the fields. The solution for our customers is to make sure that all the characters they use in the interactive form fields are defined in the font associated with the form fields and that the whole font is embedded in the PDF document. For more information on how to embed fonts in PDF Studio see How to Embed Fonts in a PDF Document.

If you’re interested, you may read more technical details in Qoppa’s PDF developer knowledge base.