Master PDF Editor allows you to create, edit, preview, encrypt, sign
and print XPS and interactive PDF documents.
It's powerful editing features allow you to convert between PDF and
XPS formats, add interactive controls such as buttons, text fields,
check boxes, and event handlers to your documents, split and merge
PDF files.

The Linux-based version is free for non-commercial use.

This is version 4, which still saving without a watermark from the trial
version. If you are looking for the latest version of the program, look
for "MaterPDFEditor", instead.