问题
I'm wondering if it is possible, using iText (that I used for signing) or other tools in Java, to add biometric data on a pdf.
I'll explain better: while signing on a sign tablet, I collect signature information like pen pressure, signing speed and so on. I'd like to store those informations (variables in java) togheter with the signature on the pdf. Obviously hidden and encrypted such as the signatures info.
Is there some kind of hidden data field on a pdf or something that can contain this kind of information? I think it is inappropriate to store it in the metadata fields such as author etc.
回答1:
There are different ways to add info to a PDF document.
You could add the data in a document-level attachment. That way, people can inspect the data by opening the attachment panel.
Storing it as metadata is fine too, but you're right about it being inappropriate to store that info in something like the author key.
As you may know, the /Info dictionary will be deprecated in PDF 2.0 in favor of using an XMP metadata stream. In this metadata stream, you can add custom XML data (see section 2.2.1 of the XMP specification - Part 3).
If you don't want to mix your biometric data with the document metadata, you can even define an XMP stream for any dictionary you want, probably including the signature dictionary. See section 14.3.2 of ISO-32000-1.
PS 1: I don't know who downvoted your question. I upvoted it, so you're back at 0.
PS 2: If you want to create future proof signatures, read http://itextpdf.com/book/digitalsignatures
PS 3: Signatures created with the 4-year-old version of iText usually aren't future-proof.
来源：https://stackoverflow.com/questions/16957941/attach-hidden-biometric-data-to-a-digital-signature-on-a-pdf