There is no such limit. What's your use case?
It probably sounds outrageous but I'm considering making a form with 2,800 fields. A private cemetery wants to convert their hand-written 36" x 63" layout to digital form. It needs to be filled-in with current data and also updated in the future with new data by non-technical people. I've tested this form using a layout created in Illustrator, printed to a PDF, opened and edited in LiveCycle then uploaded to my Adobe account using "Distribute." It will take a while to add all the fields. I didn't want to find out the really hard way that the limit was less than my needs.