Usage of Acrobat Fillable Form?

Before Acrobat DC, if you Reader-enabled a form with Acrobat and distributed the form to more than 500 recipients, you could use data from no more than 500 instances of the enabled form (including hardcopies) that were returned to you. There never was a limit on how many times a form could be used or on how many people could use a form. Acrobat DC has no such restrictions.

Essentially, no.

However, Adobe did seriously restrict the capabilities of Reader. In order to overcome those restrictions, Adobe developed the Extended Rights, and the according tools "Reader Extensions". The "full" Reader Extensions server was (and still is) sold for a very steep amount of money. There is, however, the possibility to add some extended Rights using Acrobat Pro. In this situation, there are limitations (such as 500 uses of that form).

This was correct until Reader XI. Reader XI and newer no longer need the Extended Rights, and therefore, those limitations no longer apply.

If you want to really be sure, read the Acrobat EULA.

Hope this can help.