Was the PDF form sent via email and opened in Apple Mail preview on iPad?
Please note that Apple Mail's preview does not render form fields correctly, which makes it look like your PDF form is blank or empty.
Would you make sure to open the PDF form in Acrobat Reader for iOS?
Please take a look at the Mail section of the following FAQ document. It describes how to use the iOS "Open In" feature.
Please let us know if you have additional questions.