A major component of NPD is it’s harm to the sufferer’s interpersonal relationships. I think the behaviors that contribute to this, though diagnostically and medically relevant, are generally deservedly stigmatized.

This is, of course, different from the armchair diagnosing someone with NPD just because they exhibit some of these behaviors, which I do think contributes significantly to the stigma of mental illness.

Ultimately, someone with NPD is more than their diagnosis and can certainly be capable of interpersonal relationships that are worthwhile to all parties involved.

I have personally used DrawboardPDF on Windows tablets because it came with one that I bought, but it costs money and there may be better options out there. Nonetheless, it’s probably worth checking out.

Aside from that, I would probably consider looking at Xournal++. It’s technically a note taking program, so probably not quite what you’re looking for, but it handles PDFs and it seems to work well with a stylus. I’ve never used it to any significant extent, however. It’s also free, open source, and cross platform which are major pluses.