Fillable PDF forms

The NZ Government Web Standards require that if you use PDF, you must provide an accessible alternative, whether this be accessible HTML or an accessible Word document or another accessible format.

https://webtoolkit.govt.nz/standards/nzgws-2/technical/#may

For instance, you might provide the PDF version (fillable or not, but preferably both), along with a simple TXT version of the form.

For example, see how the Canadian Government deals with its forms: http://www.cra-arc.gc.ca/formspubs/t1gnrl/nnrsdnts-eng.html.

Or another example of accessible alternative txt form (compare the PDF and the .txt): http://www.cra-arc.gc.ca/E/pbg/tf/t2200/README.html