There's also this website which I've used successfully with many bureaucracies.
EDIT: Clicking on it, I see the source code is available. If I can run it on my local box then this might be a little less nasty than mucking with the `convert` command.
Github repo: https://github.com/baicunko/scanyourpdf
But yeah, the security implications of uploading a PDF with your SSN and signature to a random website is, um, not good.