Hello Sebastian,

I do not have a copy of PrimoPDF here to try out, but there is a good chance that the "weighted" (thick) staff line problem can be corrected.

Make sure that the pixel resolution that you specify to be used by the PDF driver is the same as the real pixel resolution used by your real printer.

Don't worry if in Composer's Page View you see uneven thick staff lines. That might happen for reasons that are complicated to explain. If you like to edit the score in Page View rather than Window View, then chose another printer driver than the PDF printer driver during your editing activities. Then, select the PDF printer driver only when you are actually printing to the PDF file.

Please let us know if the above tips help.

Cheers
-- Mark