Honestly, I'm not sure. This is really more of a client issue than a servlet one. You could try the General Computing forum on this site but I suspect you would get faster results by googing or going to Adobe's site.
Adobe PDF Reference v 1.6 - a 8.9MB pdf document has a section on forms - it looks very detailed at the document structure level. The Apache FOP toolkit for PDF does not seem to address forms so generation from a servlet seems unlikely. I think you will need a commercial Adobe product to set up forms. Bill