Improve recognition of form fields: HTML > PDF > Recognise form fields

I have an HTML page that I export as a PDF and then try to recognise via form fields.

This works more bad than good. I wonder if there are any rules or something that must be observed specifically so that form fields are also recognised as form fields.

Can anyone help me with this? Does anyone have experience with this?

I haven't found a page that explains exactly how the recognition works. I assume that it works visually.