Send email 'form' to be edited by recipient via mail merge?

Thought I’d got this worked out and I haven’t. And now in a rush to get this done and feeling stupid.

I have a writer doc as a form approx 6 pages long, multiple tables.
I have a base database containing individuals information to populate the form.
I want to email it to a number of people, so they can edit their data/fill in missing data .
Ideally I want it to appear in the email body text, not as an attachment - I’ve found people have problems editing attachments on mobile phones, also I don’t want them to try and print them out (I want to control the layout and I don’t want them to fill in by hand and scan them back).
The idea was sent them as html files via mail merge and save the individual docs. Then when they replied to the email I would ‘compare’ docs to check for any changes.
I have saved the form as a very long page (150cm long!) so there are no page breaks.

The problem I have is that the recipients can’t edit the form…found this out doing a test send from gmail to a gmail address
I am sure there must be a way round this - add some code to the html? Use a different format?
Or am I missing something obvious?