On the Plus Subscription details it mentions that "Form distribution and data collection with Acrobat and Form Tracker may not exceed 500 people per form".
Can you clarify exactly what this means please?
Is it a 500 limit on how many people may respond to 1 PDF questionnaire or is it a limit on how many people you may publish and share the results with?
This applies to PDF forms that have been Reader-enabled by Acrobat, not PDF forms that are enabled by FormsCentral. It's also not very accurately worded. The limitation imposed by the Acrobat License Agreement can be summarized with the following:
If a Reader-enabled form is distributed (i.e., made available) to more than 500 people, you are limited to using data from no more than 500 instances (including hardcopies) of the form that have been returned to you. If a form is distributed to 500 or fewer people, there is no limitation on the number of returned forms that you may use data from.
It isn't worded well because the license specifically states that you may distribute an enabled document to an unlimited number of recipients. The limitiation is on the number of forms you are allowed to use data from, not on the number of people you are allowed to collect forms from.