There are several nice fillable PDFs available for the RPG hobby. These have boxes that number values can be entered and simple formulas are calculated throughout the sheet. I'm finding that the programs I've tried cannot save this data. I've tried PDFEdit, XPDF, and Evince. Is there a Linux program that will save fillable PDFs? Or perhaps I'm not using the above correctly?
This page states that Evince, Okular (in a somewhat limited way), Adobe Acrobat Reader and Cabaret Stage support filling forms.
qpdfview appears the have the functionality you want with regards to saving form data.
Form data appears to be saved when I use it on Arch Linux.