Apply a form fillable "layer" on PDF files

Based on try67's suggestion, here is what worked for me:

I have paper forms that I receive that are partially filled out with information that changes from form to form, day to day.  So this one-page scanned page has fixed text that doesn't change from form to form, has some text that changes from form to form (because those parts of the form are filled in before it gets to me), and has some spaces for me to fill in and boxes for me to check.  The places for me to fill in and check are always in the same place on every form.

Starting with one of the scanned forms, I asked Acrobat DC to "Prepare Form" and Acrobat generated a set of form fields (text boxes, check boxes, etc.).  I cleaned that up, moving fields a little, giving them meaningful names, deleting things that Acrobat thought were for me to fill in but aren't, etc.  Acrobat can't tell whether three boxes are to be check boxes (e.g., each can be checked or unchecked) or a radio button set (e.g., only one can be checked at a time) so those were manually specified.

Once I had the form fields where I wanted them and cleaned up the form, I closed the "Prepare Form" ribbon and opened the "Edit PDF" ribbon.  Acrobat had parsed the content of my scanned form into various objects (text boxes, lines, etc.) and I just deleted all of those objects until all I had was a blank page with the form fields that I put there in the Prepare Form steps.  I saved that as a new file I called "form_overlay.PDF".

Now, each time I have to process a scanned form that comes as a PDF, I first open the form_overlay.PDF.  Then I select "Add Background" from the "Edit PDF" menu and under source, I select the "File" radio button and select the scanned form to be my background.  Since nothing on the scanned form itself is to be edited (all the edits are to the form overlay), that works.  Once the form fields are edited, I can just save that document.  I guess I could flatten the layers so that the background and the form fields are one layer, but I don't know why that would be needed.

I am interested in a solution to this as well.

What I think Geo5C4F wants to do is combine a scanned page and a template, with certain assumptions: (1) the scanned page is one of many scanned pages but each scanned page has form fields (text fields, checkboxes, radio buttons) that are blank, (2) the locations of the form fields do not change from scanned page to scanned page, and (3) the user has created a template PDF that has all the form fields in the right locations on an otherwise blank page.  The idea is to overlay the template onto one scanned document, allow the user or someone else later to edit those form fields, and then perhaps flatten the layers, print it, etc.  Then, for the next scanned document, the user overlays the same template over that new scanned document as well.  This avoids the need to manually add the exact same form fields in the exact same place for each scanned document.

Using "Replace Pages", the template PDF page can replace the scanned page, but the other content that was on the scanned page is no longer there.  This is the same as just opening the template PDF by itself.

I created a template PDF (a separate PDF file that is one blank page with some form fields - text, checkboxes, radio buttons, etc.) and the form behaves correctly on its own.  I can open a scanned document and then import the template PDF as a new layer, and then I can see the content of the scanned document and on top of that I can see the checkboxes/radio buttons of the template PDF.  I don't see the text form fields because those are empty, but if I typed text into those fields in the template PDF, I would see that text.  The problem is that I cannot interact with those checkboxes or text fields.

What I would like to do is open a one-page scanned document, import the template PDF as a layer that overlays the content  of the scanned document, click on checkboxes of the template, enter text in the text fields of the template, and then flatten/print/save.