Adding Blank Page to Digitally Signed PDF with iText
You seek a method to insert a blank page at the end of a digitally signed PDF document using the iText library. However, you are concerned about the impact of adding pages on existing signatures.
To fully understand the implications, let's delve into the nature of digital signatures in PDF documents.
Adobe's white paper on digital signatures in Acrobat 9 clarifies the allowable changes that can be made to a certified or signed document without invalidating the signatures. Notably, "changing page content" is consistently prohibited, regardless of the certification or signing level.
Since adding a page inherently alters the page content, this operation is not permitted. The document's signature status relies on a specific page layout and content, which is disrupted by adding a blank page.
It's important to use append mode (incremental updates) to implement any allowable changes, including adding a blank page. Other approaches, such as modifying the document directly, can irreparably damage the signature.
In conclusion, iText does not offer a straightforward method to add blank pages to digitally signed PDF documents without invalidating the signatures. If preserving the signatures is crucial, you may need to explore alternative solutions or seek an alternative PDF manipulation library.
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