The “Print” button does not send the briefing to a physical printer but saves it into a file in bms_4.34\User\Briefings directory; check the “1. Briefing Output to File” setting by going into BMS Launcher → Configuration → General → Briefing/Debriefing. The setting should be marked by default.
To get the briefings in somewhat more readable format, go into the aforementioned Configurator submenu and mark the “3. HTML Briefings”. This setting makes BMS to save briefings in HTML webpage format when “Print” is clicked on the in-game Briefing screen.
For more information, see BMS-Manual.pdf Ch 10.3.4 subchapter “Mission Builder Tools” → “Briefing”.
Thanks johku,
Note to self: RTFM! Asp.