Word – Is there a way to convert a Word document into a PDF document

Use a print to PDF driver for windows. I use Cute PDF, myself. Once you have it installed, there should be a "print as image" option as you try to print. This will force it to print as a giant image, instead of text.

You can set the not-copy flag in the pdf file using for example pdftk (there exists GUIs for it). You need to set an owner password.

But since many pdf readers ignore not-copy/not-print-flags, another option would be to convert all the text to vector paths using e.g. inkscape, but this would bloat the pdf file heavily.

In all cases, the user could use OCR-software to extract the text, so there is no safe solution.