"Export as PDF" does not allow to choose the mode "level of grey" (or wrongly black and white).
While this is absolutely essential to supply acceptable files to be printed at a printing office in printing process "offset".
Thanks you and excuse me please for my poor english !
Good idea, I think.
I haven't seen htat this is an old idea => duplicate of bug 47278
*** This bug has been marked as a duplicate of bug 47278 ***