Digital Certificate Signatures (invisible signature)

Several European countries have standards that require that PDF invoices and statements to be signed with public key encryption certificates. Have any of you integrated this signing with Create!Form/Create!Email? I checked with BottomLine and they confirmed that it's not current supported in the workflow.

My plan is to eliminate the Create!Email part of the workflow and drop the overlaid PDFs into a drop-folder where I can set up a monkey to pick up the PDF, sign it with our certificate (essentially the same certificate setup you use with a https/ssl web site) and send it to the smtp server manually after signing.

You can use Adobe LifeCycle services to do much the same thing, but the product is far more costly than would be justified for most business cases. I'm looking to use the iText java libraries and a little custom programming to sign the PDFs.

Feedback and notes appreciated.

In follow-up to the above post, I've decided to go the 'custom component' route and drop the overlaid PDFs to a folder after C!F processing and use a custom application to sign the PDFs before delivery. Though I haven't put the finishing touches on the signing component yet, i'm committed to using the iText java libraries to implement it. I recommend using this library since it seems to be the most mature and feature-complete option out there at the 'non-enterprise-class' price point (iTextLib is open source.)