Ask HN: Best resume format for auto-fill online job apps?

Numerous online application systems have you first upload a resume in .docx, .pdf, .txt, from which an attempt is then made to pre-fill out much of the online application. This doesn't work very well and basically requires one to complete the entire app. Anyone out there have experience creating these programs? How do they work and what's the best way to format a resume so that they work properly?