I've created a simple PDF form in Acrobat DC Pro. The form consists of 2 inputs, first name and last name. I've ran the PDF through the accessibility checker tool in Acrobat and fixed all issues. I've also tested in various screen readers. At this point the PDF is 100% accessible.
I then entered some dummy data in the form in Acrobat (just text in text inputs) and flattened the form (using preflight).
When I run the flatten document through the Acrobat accessibility checker it reports that the entered form values are untagged. As you would expect, these untagged values are not read by any screen reader either (tested in Voiceover, NVDA and JAWS).
Is it possible to keep the entered form data correctly tagged when flattening a PDF form so that the PDF is accessible following the flatten?
Flattening means that all annotations (and form fields are annotations) are merged into the base document. Therefore, it is absolutely correct that you lose the fields, and their contents becomes part of the base.
The question is, however, what do you want to accomplish by flattening the document?