PDF engine wkhtmltopdf does not use specified margins

This issue cannot be reproduced in the public demo, because "wkhtmltopdf" does not seem to be installed.

To reproduce the issue in a local environment:
1) Activate the use of wkhtmltopdf at the screen /civicrm/admin/setting/misc?reset=1

2) Choose the action "Print PDF Letter" for either one person or many.

3) Click to expand the area labeled "Page Format" and fill in a top margin and left margin.

4) Click "Make PDF Letters". You will see the margin settings were ignored when viewing the PDF document.

If you deactivate the use of "wkhtmltopdf", then try creating the PDF letter again you will see that the margin settings are honored.