[OS X TeX] missing ligatures from included pdf

[Jan Hegewald]

Dear all,
I have a drawing done with Omnigraffle, saved as pdf. Herein I have placed some labels using the "Latin Modern Sans" regular font. This I want to \includegraphics in my Latex document. If I typeset, the resulting pdf is missing the ligatures from text of the Omnigraffle pdf.
Does anyone know a solution to this? I would like to use the pdf, not e.g. a png from Omnigraffle. Currently I do not even know if this is a problem with Omnigraffle, Latex or my Mac OS.

Many TIA,
-- Jan