How Can I Add a Blank Page to a Digitally Signed PDF in Java Without Invalidating the Signature?

Dealing with Blank Pages and Digital Signatures in PDFs Using Java

You're aiming to insert a blank page at the end of a digitally signed PDF using the iText library. However, you're concerned about whether adding pages will invalidate the existing signatures.

To address this concern, let's delve into the context provided by Adobe's technical white paper on Adobe Acrobat 9 Digital Signatures, Changes and Improvements. The section "Allowed and disallowed changes" clarifies the changes that can be made to a digitally signed document without compromising its validity.

According to Adobe, changing page content is consistently categorized as "Disallowed." Adding a blank page would fall under this category because it introduces a new page, altering the document's original content. Consequently, such an action is considered invalid.

Furthermore, even if not explicitly mentioned in the white paper, instantiating page templates is likely permitted in situations where form fill-ins are allowed. However, this approach requires careful preparation of the document before signing.

It's crucial to note that even the allowed changes must be implemented using append mode or incremental updates. Any other method could permanently damage the signature.

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