If you are generating read-only dynamic PDFs, there are no additional licensing requirements (apart from what you have already paid for AEM Forms).
You need additional licensing (called Reader Extensions) if your requirement was to generate an Interactive PDF (with form fields) and wanted ability to Save the PDF with filled data.
I'm not clear on what a read-only dynamic PDF is. Like, you can use it but not save it with data entered? Or you can't save it as a dynamic PDF but as a static one? I'm not even sure how to go about forcefully implementing the latter.
So distributing a fillable dynamic PDF with information already in the fields is a no-no. But if I take that form and have digital signatures which lock all of the form fields with all of the filled out data, and then distribute the PDF, that should be okay...?
If you own a license of "AEM Forms 6.1" then you are licensed to create "save off line" dynamic PDF's that can be filled in and saved / submitted offline. This used to be licensed as a separate "Reader Extensions" license but is now incorporated into your forms license. Your license is likely a CPU license so there'd be no restrictions on the number of forms you could generate. However, you will have your own EULA that describes how you can use the product and if there are any restrictions to the number of seats. There is a possibility that your EULA is unique and has some special use case restrictions so I'd check with the person / people responsible for the licensing of AEM in your organization. They should be well aware of the license.