Cannot save embedded pdf file in pdf form - you cannot save the form

I have a PDF form which has another pdf form as an attachment.,

Idea is that if a certain criteria meets, user can open this embedded form and fill it out and save.

Now I am stuck at "Please fill out the form.  You cannot save the data typed into this form.  Please print your completed form if you would like a copy for your records" in acrobat reader. I have changed the file type using acrboat dc to "save as other - Reader extended PDF - Enable forms fill in & save in acrobat reader, however nothing changes. I am using Acrobat DC version.  Would really appreciate your help in this as i want the user to save the attachment within the form itself afetr making changes without having to reattch the document.  If there is a way aroud it using a script, please assist if that's the case.