I am using iText 7.2.4 to develop a PDF document signing service with Java Spring. I am asked to allow the user providing multiple PDFs in a single call and return all the PDFs signed. The problem is that to compute the signatures (to sign the hashes of the documents) I have to use a service that recieves all the hashes at the same time and returns them signed, and I do not know how do I have to include them to the PDFs to return the documents signed with a valid signature.

I have tried to sign a single PDF using the PDFSigner class which allows using an IExternalSignature with a custom implementation (in my case I call the service previously mentioned) for signing the hash of the document, and that works, but is a method that only allows signing a single document, so I would like to know if there is a way of doing what I have said before.