view signed version with not embedded font

Hi. I have a PDF document with Verdana font which is not embedded. There are also cyrillic symbols, not sure does it make sense. After I signed this PDF everything  looks great until I try to view signed version: there is blank instead of cyrillic symbols. Actually there are non-printable symbols in a strange encoding which I can for example copy.

Is it a bug?

Is there workaround for this issue?