Hi,
I have 8 years experience in digital signature.
I have created many apps, service, web service,.. to sign pdf document by java, C#, C++,....
I understand your requirements, if you need bulk signing documents use Usb, we need to sign with Usb Token by Pkcs#11 interface, I have an project semilar this, I assurance I can do it..
Please check my profile, I am done many project about digital signature in the Freelancer.
Contact me if you interested!
Thanks for reading!