We are trying to create a fillable PDF with Adobe Reader, I think, and seems to be working but we can’t create calculations in it. Do we need a special version of Acrobat for this?
Acrobat Pro has had forms with calculations a long time. It’s not freeware, but quite a premium piece of software.
Search for “PDF form calculations” or “PDF forms with calculations”, You get plenty of quidance to choose from. An example: https://acrobatusers.com/tutorials/print/how-to-do-not-so-simple-form-calculations
The same search gives also several hints how to use freeware.
Foxit Phantom presents itself as a low cost alternative for Acrobat. It also has forms with calculations. I haven’t tested it.