Hi Matadem, do you mean a background image that was added using the View > Image command?

Sorry no - the background image function is designed to be used as a modeling aid for a reference to trace over. They do not export out to PDF.

You would probably need to add it in a 2D vector drawing package like Affinity Designer or Adobe Illustrator.

re:
> Also adjusting image on the fly (scaling without aspect ratio would be a nice addition in future).

Images are designed to keep their aspect ratio when resized. You might try this plugin though that can modify the aspect ratio:
http://moi3d.com/forum/messages.php?webtag=MOI&msg=10730.7

- Michael