signature – How to digitally sign a PDF with a usb etoken?

I’m trying to digitally sign a complex PDF that already has a bunch of other trusted signatures, with my own signature?

On Windows and Mac I would use adobe reader, open the pdf, draw a rectangle place where the signature would show up and then sign it with my USB token.

On Ubuntu I can’t do that since I have no access to adobe reader. I managed to get my etoken to show up in Ubuntu though.

Can anyone recommend a rather painless method of achieving this goal?