OpenESF is licensed under the AGPL (aside from its commercial license)
and generally speaking is free to use. My impression is that such a
usage as you describe would be okay. You would need to provide a link
to the version of the code you are using, though, so that others who do
have access to your OpenESF system can also get access to that version
of the source code.
We're not lawyers, and Yozons has never sued anybody before, but I think just providing the version you are using and a link to
open.esignforms.com
would suffice for providing access to the source code if you are
running an unmodified version. But if you do modify it, then you do
need to make that modified code available for others. If at all
possible, we hope that you contribute such modifications to become part
of the core if it's generally useful so the product keeps on improving
for everyone.
Note that your form/document that you build is no longer considered to
be programming changes to OpenESF (we consider it to be just data, which
you own if you created it, even if some may be "code" like HTML/JSP),
so you do not have to provide that unless you want to. If you have an
interesting form that you think others might like, we'd be happy to take
a copy when you are done and include it in our free forms area on our
demo system (forms can be exported from libraries easily so others can
the import it).
Of course, we hope that you'll give OpenESF credit to help us grow our community.
Good luck!