Adding to @willamansley comments:
Creating PDF forms would usually be done in Adobe Acrobat (the full product not the reader), or perhaps any similar PDF-creation tool capable of creating the form functionality of a PDF document.
I don't know if Joomla has anything that can create PDF forms (there are things that create PDF documents for Joomla, but your question would be better asked on the Joomla forum - https://forum.joomla.org as this is not a Machform issue as I see it.