If you’re proud of the work you did, and want the entire world to see it (assuming the client doesn’t click X when writing his review), delivering a PDF is the only way to do it.
I deliver both a Microsoft Word document and a PDF, it’s something I started doing yesterday after realizing that buyers aren’t just looking at your old portfolio samples, but they want to see what you did recently.
Just be aware that if the work you’re delivering isn’t perfect, other people will see the mistakes you’ve made.
So only deliver a pdf is you’re really sure of yourself.
As for issues of client confidentiality, that’s up to the client. He or she can click X and delete the sample.