Hi Erich,
Thank you for your interest in Essential PDF. Take a look at the following link to create a Self-Signed Digital ID [pfx file]
http://www.markszulc.com/articles/createDigitalID.html
Regarding the error with digitally signing the document I am afraid I was unable to reproduce it, can you please take a look at the following flow model sample
DigitalSigning.zip
and let me if the problem still exists.
Best Regards,
Ajish.