What sort of expert do I need?

I'm a lawyer and I have a digital document that is a suspected forgery in a case I'm involved in. I am aware that there are Questioned/Forensic Document Examiners, but my understanding is that they are primarily concerned with physical documents, including forged signatures and handwriting. In my case, the suspected forgery is currently a digital document in PDF format. What kind of forensics expert do I need to provide expert testimony concerning a suspected forged PDF document?

computerforensics expert sort