[magnat]

We have tax forms available as interactive PDFs, which:

   * auto-computes formulas
   * enables and disables whole sections of the document depending of filled values
   * performs complex validation, beyond checking for required fields and regexp patterns
   * offers inline help
   * can be filled, saved and printed completely offline
   * when printed, looks exactly the same as traditional, paper form
   * don't require external software beyond a PDF reader

[HeavenFox]

NY tax form also generates a barcode from the information you entered to facilitate faster processing

[cookiengineer]

Why is this an interactive PDF in the first place?

[niutech]

To be able to print it and fill in by hand or by typing on a PC? To be able to save the filled-in form in a portable file?