Before we get the inevitable "Why are you using Adobe Reader?!" Plenty of rich PDF forms, including those used by the US government, require the use of "real" Adobe Reader to work correctly.

Without it you can still fill in the form but validation is complete, signing is missing, direct submission doesn't function, and dynamically generated content (like QR codes) don't work.

Adobe Reader is pretty mandatory if you are doing anything more with a PDF than hitting the print key.