So a guy wants me to make him some interactive PDFs. No problem.

Now I've learned more details and not even sure its possible.

He wants a PDF that he can partially fill out, save it and send it to a client to fill the rest out. Except he wants the parts he fills out to be protected so the client can't change them, and he doesn't have Acrobat.

Is this possible and if so how would you suggest doing it?

It sounds like it is possible. links

Looks like you can build a button as part of the form that locks down sections, so in theory your guy can do his bit... hit the button to lock his responses then send it on for the client to fill out.

I've done a bit with pdf forms over the years and it ain't much fun. Is your client set on pdfs? Surely you could do similar with a web based form?