Michael, is it possible to export, with the hidden line feature, some objects set to wireframe? Because I have a model with some glass elements and I would like them to be in wireframe after the export, so I can see through them..

Now you can from a model select only lines by the Browser (so the wireframe)
and export them to PDF
Put hidden line to 0

Thanks, that's what I needed!

Select the edges and volumes you want
here a cube in front of a Sphere
Don't render Hiddenlines
Cube is like transparent!
PDF result

Yup like Pilou says, if you have an object's edges selected and then do a File > Export, just those selected wireframe edges of that object will get exported instead of the entire solid object.

- Michael