When you try to open a PDF document with true type fonts you get a Windows style pop-up error "Cannot extract the embedded font '<TTF font name>'. Some characters may not display or print correctly."
This occurs when you use a TTF font with the option 'Do not insert font in PDF' and the font is not installed on the Windows PC you use to open the PDF.
When importing the true type font, setting the flag 'Do not insert font in PDF' means that only the font name and not the font itself is put into the PDF file. That means the font is not embedded into the PDF file any more, only the font name of the Windows font is put into the file. This works, if the Windows font (for example Arial) is installed on the PC which you use to display the PDF file and if you use at least Acrobat Reader version 6.0.