Can I Add Blank Pages to a Digitally Signed PDF Without Invalidating the Signatures?

Adding Blank Pages to Digitally Signed PDFs

Question:

Can blank pages be inserted into a digitally signed PDF using iText without invalidating the existing signatures?

Answer:

According to Adobe's technical white paper on digital signatures, adding or changing page content is generally not permitted for certified documents. As adding a blank page modifies the page content, it could potentially invalidate existing signatures.

Detailed Explanation:

Adding blank pages may invalidate digital signatures because such changes alter the integrity of the document's page layout. Adobe specifies the following actions as disallowed for certified documents:

• Digitally signing
• Adding or editing annotations
• Adding form fields
• Changing page content

Exceptions and Considerations:

In some cases, certified documents may allow certain changes, such as form fill-ins and annotations. However, even these changes must be made in append mode (known as incremental updates) to avoid invalidating the signatures.

Implications:

If you wish to insert blank pages into a digitally signed PDF without invalidating the signatures, you must ensure that other options, such as page templates or preparing the document before signing, are not viable.

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