We are currently working on implementing tab advance for some custom PDFs we use in our iOS application. The requirement is only to be supported with an attached hardware keyboard, so no need for an input accessory view.
I've been mucking about with the provided FormFillTool to get the desired functionality, but haven't been making much progress. I can get the current UITextField, detect the hardware tab key press, find the next field, and fire a custom event back to the parent PDFViewCtrl instance. After that things get murky.
There are undocumented API calls to simulate a touch event, but that route would most likely lead to rejection of the app for Apple App Store deployments. The sample code is excellent in regards to iterating through the fields in a batch fashion. I just don't see a clear path to be able to advance to the next available text field.
Any thoughts, ideas, or alternative approaches would be greatly appreciated.