When the texts are exported into pdf, the TTF fonts can be exported two ways.
Just reference to the font, so pdf viewer should find this font in the system when open the pdf file.
Whole TTF font file is exported into pdf. This leads to increasing file size but pdf viewer will open the font from the pdf and render the text as it should be rendered - so there will be no portability problems.
Pdf export does not collect the fonts from the drawing at all, it collects them from the system. This flag makes pdf export to embed the whole font files into pdf file.
More info in documentation about pdf export parameters.