digital signatures for part of workbook

[bruderbell]

Hi
I'm trying to figure out a solution to be able to digitally sign a portion of a document, but leave the rest open for editing. So maybe user 1 would enter info into sheet 1, then sign sheet 1, then pass the document to user 2. User 2 would enter some info on sheet 2, then sign sheet 2, pass to user 3. And so forth.

Is there a solution out there for this? I'm signing with PKI Certs.

Thanks in advance.