I'm one of the developers working on pdf.js. Can you elaborate a little more about what feature you're worried about? We want to take any privacy concerns very seriously. That said if you feel we are missing something feel free to start an issue on our github page or send mail to our mailing list https://github.com/andreasgal/pdf.js . The nice thing about the project is it is automatically sandboxed since everything is in javascript.

It definitely still is a work in progress, but if you find a problem please file an issue on https://github.com/andreasgal/pdf.js . We are working hard to support more PDFs, but the spec is huge (over 1000pages) so it will take some time.

There's also another open source PDF project called Trapeze. It currently works in firefox, safari and chrome. Demo at: http://trapeze.xyrka.com/ Project at: http://code.google.com/p/trapeze-reader/ I even posted it to slashdot awhile back, but it never made it to the front page... http://slashdot.org/firehose.pl?op=view&id=17924850