Need a module for an iPhone app that will be able to detect lines or boxes in pdf where user is required to input or give signature. (Even if the PDF was created with no user-editable text areas)

for example, look at this PDF: http://www.irs.gov/pub/irs-pdf/fw4.pdf
if you click in a blank area, a textbox actually pops up that lets you fill in the value
i'm sure there's probably a way to detect that programmatically even if the PDF has not been programmed for form entry.

Will also need to highlight the forms and then be able to user back/next keys on iphone keyboard to move between each field. Just like in a pdf and fill each form.

Any API used must be valid with Apple iPhone SDK so hat it can be approved for sales on iTunes App Store.