I will ask what we can improve about printing from the web browser. But that is a difficult thing…
As Jürgen has already pointed out: You achieve the best results with your own print templates in the form of Office documents.
This is certainly more work at first, but then it is worth it.
I recently gave a lecture on Collabora Online in EGroupware. I have translated the slides into English:
In it you will also find the topic document merge. Among other things, the modules in which this is available. You can always orientate yourself on whether the placeholders are offered in the sidebar.
Please note that we here in the Community Forum can only provide very limited support in this area.
Stefan