Print PDF as-is, no scaling, no added margins
Print settings, scale 100%

Ok, I read your question, I have read your comment on @user2236575 answer. Still I am going to point you in the same direction.

This is what you need to do for printing without resizing:


Open your PDF in Preview. 
Select 'Print...' in the File menu, or press CommandP
Within the 'Print' settings window, set the scale to 100%
and press 'Print' to print at 100% of the original PDF


To check this, I have added a PDF file containing a ruler: download PDF ruler

Print this PDF with the instructions above. 

Test your print like this if you do not have got a ruler. An A4 size 29,7cm long and 21,0cm wide. Overlay the wide side of an A4 paper over your ruler, it will measure 21cm exactly.

If not, you did print it correctly, but your printer does something wrong or overwrites these settings.