Is there a package and command that can secure rendered pdf with a password?
There used to be a package achieving PDF encryption, but it relied on obsolete pdfTeX patches:
Nowadays, you need an external tool to encrypt your PDF. Here is an example to encrypt a PDF with
That said, I guess a LaTeX package could be done to make use of
Just please remember that no PDF encryption is really bullet-proof. Once the user can see the PDF, then he can print it and edit it. It can just require the use of other tools than the Adobe thingies.
In the case of pdfTeX, an external tool, such as pdftk or qpdf, is necessary to encrypt. In the case of XeTeX, we can use a \special supported by xdvipdfmx, for example: