How to make an incremental update to a PDF

I need to make an incremental update (add some existing pdf pages) to an signed pdf, making the included signature still be valid (that cover the first page).

I've seen some post's telling that is possible with PDFStamper开发者_如何学Go (iTextSharp), but I'm unable to find a example out to make it append.

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Changing an already signed PDF would sound imply a security leak in the PDF signing functionality/spec. The purpose of signing a PDF is a guarantee to the reader that it has not been altered by anyone other than the original author.

I think your only option is to send extra pages in a seperate PDF, or change the original PDF and have it re-signed.