Documents with watermarks

We are looking for a new extension to offer documents for download. We have the requirement that the documents (PDF) are only made available to certain users after registration. I can realize this with Dropfiles. All users should be able to view the documents with a watermark. So far, we have created a second version of each document that has a watermark.
Now my questions:
1. Does Dropfiles have the possibility of a preview without authentication?
2. Is there a function in Dropfiles so that watermarks are automatically created on the documents?

I look forward to an answer.